Method and apparatus for uplink multi-user transmission in a high efficiency wireless lan

ABSTRACT

Methods and apparatus for transmission opportunity limits, backoff procedures, uplink random access related to uplink multi-user transmission in a High Efficiency WLAN (HEW) are described. An embodiment is a method for performing a frame exchange sequence including an uplink multi-user (UL MU) transmission by an access point (AP) in a wireless local area, the method including acquiring a transmission opportunity (TXOP) for initiating the frame exchange sequence; determining if a time required for the frame exchange sequence not including a control response frame exceeds a TXOP limit; and transmitting a trigger frame to one or more stations (STAs) when the time required for the frame exchange sequence not including the control response frame does not exceed the TXOP limit.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation application of U.S.application Ser. No.

15/136,803, entitled “METHOD AND APPARATUS FOR UPLINK MULTI-USERTRANSMISSION IN A HIGH EFFICIENCY WIRELESS LAN,” filed on Apr.22, 2016,which claims the benefit of priority under 35 U.S.C. § 119 from U.S.Provisional Application No. 62/151,966, filed on Apr. 23, 2015, U.S.Provisional Application No. 62/159,170, filed on May 8, 2015, U.S.Provisional Application No. 62/181,725, filed on Jun. 18, 2015, U.S.Provisional Application No. 62/183,688, filed on Jun. 23, 2015, U.S.Provisional Application No. 62/205,577, filed on Aug. 14, 2015, and U.S.Provisional Application No. 62/307,033, filed on Mar. 11, 2016, theentirety of each of which is incorporated herein by reference.

BACKGROUND Technical Field

The present disclosure relates to Wireless Local Area Networks (WLANs),and more particularly, to a method and apparatus for uplink multi-usertransmission in a High Efficiency WLAN (HEW).

Related Art

Along with the recent development of information and telecommunicationtechnology, various wireless communication techniques have beendeveloped. Among them, the WLAN enables a user to wirelessly access theInternet based on radio frequency technology in a home, an office, or aspecific service area using a portable terminal such as a PersonalDigital Assistant (PDA), a laptop computer, a Portable Multimedia Player(PMP), a smartphone, etc.

To overcome limitations in communication speed that the WLAN faces, therecent technical standards have introduced a system that increases thespeed, reliability, and coverage of a wireless network. For example, theInstitute of Electrical and Electronics Engineers (IEEE) 802.11nstandard has introduced Multiple Input Multiple Output (MIMO) that isimplemented using multiple antennas at both a transmitter and a receiverin order to support High Throughput (HT) at a data processing rate of upto 540Mbps, minimize transmission errors, and optimize data rates.

In recent times, to support increased numbers of devices supportingWLAN, such as smartphones, more Access Points (APs) have been deployed.Despite increase in use of WLAN devices supporting the Institute ofElectrical and Electronics Engineers (IEEE) 802.11ac standard, thatprovide high performance relative to WLAN devices supporting the legacyIEEE 802.11g/n standard, a WLAN system supporting higher performance isrequired due to WLAN users' increased use of high volume content such asa ultra high definition video. Although a conventional WLAN system hasaimed at increase of bandwidth and improvement of a peak transmissionrate, actual users thereof could not feel drastic increase of suchperformance.

In a task group called IEEE 802.11ax, High Efficiency WLAN (HEW)standardization is under discussion. The HEW aims at improvingperformance felt by users demanding high-capacity, high-rate serviceswhile supporting simultaneous access of numerous stations in anenvironment in which a plurality of APs is densely deployed and coverageareas of APs overlap.

No specified methods or apparatus for transmission opportunity limits,backoff procedures, uplink random access related to uplink multi-usertransmission in High Efficiency WLAN (HEW) have been provided.

SUMMARY

The present disclosure describes embodiments of a method and apparatusfor transmission opportunity limits, backoff procedures, uplink randomaccess related to uplink multi-user transmission in HEW.

The embodiments contemplated by the present disclosure are not limitedto the foregoing descriptions, and additional embodiments will becomeapparent to those having ordinary skill in the pertinent art to thepresent disclosure based upon the following descriptions.

In an aspect of the present disclosure, a method for performing a frameexchange sequence including an uplink multi-user (UL MU) transmission byan access point (AP) in a wireless local area may be provided. Themethod may include acquiring a transmission opportunity (TXOP) forinitiating the frame exchange sequence; determining if a time requiredfor the frame exchange sequence not including a control response frameexceeds a TXOP limit; and transmitting a trigger frame to one or morestations (STAs) when the time required for the frame exchange sequencenot including the control response frame does not exceed the TXOP limit.

In another aspect of the present disclosure, an AP apparatus forperforming a frame exchange sequence including an UL MU transmission ina wireless local area may be provided. The AP apparatus may include abaseband processor, a transceiver, a memory, etc. The baseband processormay be configured to acquire a TXOP for initiating the frame exchangesequence; determine if a time required for the frame exchange sequencenot including a control response frame exceeds a TXOP limit; andtransmit a trigger frame to one or more STAs when the time required forthe frame exchange sequence not including the control response framedoes not exceed the TXOP limit.

In another aspect of the present disclosure, a non-transitorycomputer-readable medium having instructions executable for an AP toperform a frame exchange sequence including an UL MU transmission in awireless local area may be provided. The executable instructions maycause the AP to acquire a TXOP for initiating the frame exchangesequence; determine if a time required for the frame exchange sequencenot including a control response frame exceeds a TXOP limit; andtransmit a trigger frame to one or more STAs when the time required forthe frame exchange sequence not including the control response framedoes not exceed the TXOP limit.

It is to be understood that the foregoing summarized features areexemplary aspects of the following detailed description of the presentdisclosure and are not intended to limit the scope of the presentdisclosure.

According to the present disclosure, a method and apparatus fortransmission opportunity limits, backoff procedures, uplink randomaccess related to uplink multi-user transmission in HEWcan be provided.

The advantages of the present disclosure are not limited to theforegoing descriptions, and additional advantages will become apparentto those having ordinary skill in the pertinent art to the presentdisclosure based upon the following descriptions.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the disclosure and are incorporated in and constitute apart of this application, illustrate embodiment(s) of the disclosure andtogether with the description serve to explain the principle of thedisclosure. In the drawings:

FIG. 1 is a block diagram of a Wireless Local Area Network (WLAN)device;

FIG. 2 is a schematic block diagram of an exemplary transmitting signalprocessing unit in a WLAN;

FIG. 3 is a schematic block diagram of an exemplary receiving signalprocessing unit in a WLAN;

FIG. 4 depicts a relationship between InterFrame Spaces (IFSs);

FIG. 5 is a conceptual diagram illustrating a procedure for transmittinga frame in Carrier Sense Multiple Access with Collision Avoidance(CSMA/CA) for avoiding collisions between frames in a channel;

FIG. 6 depicts an exemplary frame structure in a WLAN system;

FIG. 7 depicts an exemplary HE PPDU frame format.

FIG. 8 depicts an exemplary High Efficiency (HE) Physical layer ProtocolData Unit (PPDU) frame format according to the present disclosure;

FIG. 9 depicts subchannel allocation in a HE PPDU frame format accordingto the present disclosure;

FIG. 10 depicts a subchannel allocation method according to the presentdisclosure;

FIG. 11 depicts the starting and ending points of a High Efficiency LongTraining Field (HE-LTF) field in a HE PPDU frame format according to thepresent disclosure;

FIG. 12 depicts a High Efficiency SIGnal B (HE-SIG-B) field and a HighEfficiency SIGnal C (HE-SIG-C) field in the HE PPDU frame formataccording to the present disclosure;

FIG. 13 depicts another example of a HE PPDU frame format according tothe present disclosure;

FIG. 14 depicts an exemplary HE PPDU frame format for a wide channelband according to the present disclosure;

FIG. 15 depicts another exemplary HE PPDU frame format according to thepresent disclosure;

FIGS. 16 and 17 depict operating channels in a WLAN system;

FIG. 18 depicts an exemplary operation of TXOP limits for UL MUtransmissions according to the present disclosure;

FIG. 19 depicts an exemplary frame exchange sequence with TXOP limitsfor UL MU transmissions according to the present disclosure;

FIG. 20 depicts another exemplary frame exchange sequence with TXOPlimits for UL MU transmissions according to the present disclosure;

FIG. 21 depicts another exemplary frame exchange sequence with TXOPlimits for UL MU transmissions according to the present disclosure;

FIG. 22 depicts another exemplary frame exchange sequence with TXOPlimits for UL MU transmissions according to the present disclosure;

FIG. 23 depicts an exemplary operation of backoff procedure for UL MUtransmissions according to the present disclosure;

FIG. 24 depicts an exemplary operation of backoff procedure for ULrandom access according to the present disclosure;

FIG. 25 depicts an exemplary operation of UL random access in DFSchannel according to the present disclosure;

FIG. 26 depicts an exemplary RF combining mechanism for enhancedmulticast and broadcast service according to the present disclosure.

DETAILED DESCRIPTION

In the following detailed description, certain embodiments of thepresent disclosure have been shown and described, by way ofillustration. As those skilled in the art would realize, the describedembodiments may be modified in various different ways, without departingfrom the spirit or scope of the present disclosure. Accordingly, thedrawings and description are to be regarded as illustrative in natureand not restrictive. Like reference numerals designate like elementsthroughout the present disclosure.

In a Wireless Local Area network (WLAN), a Basic Service Set (BSS)includes a plurality of WLAN devices. A WLAN device may include a MediumAccess Control (MAC) layer and a PHYsical (PHY) layer according toInstitute of Electrical and Electronics Engineers (IEEE) 802.11 seriesstandards. In the plurality of WLAN devices, at least one the WLANdevice may be an Access Point (AP) and the other WLAN devices may benon-AP Stations (non-AP STAs). Alternatively, all of the plurality ofWLAN devices may be non-AP STAs in an ad-hoc networking environment. Ingeneral, AP STA and non-AP STA may be each referred to as a STA or maybe collectively referred to as STAs. However, for ease of descriptionherein, only the non-AP STAs may be referred to herein as STAs.

FIG. 1 is a block diagram of a WLAN device.

Referring to FIG. 1, a WLAN device 1 includes a baseband processor 10, aRadio Frequency (RF) transceiver 20, an antenna unit 30, a memory 40,which may be or may include a non-transitory computer-readable medium,an input interface unit 50, an output interface unit 60, and a bus 70.

The baseband processor 10 may be simply referred to as a processor, andmay perform baseband signal processing described in the presentdisclosure, and includes a MAC processor (or MAC entity) 11 and a PHYprocessor (or PHY entity) 15.

In an embodiment of the present disclosure, the MAC processor 11 mayinclude a MAC software processing unit 12 and a MAC hardware processingunit 13. The memory 40 may store software or machine-executableinstructions (hereinafter referred to as ‘MAC software’) including atleast some functions of the MAC layer. The MAC software processing unit12 may execute the MAC software to implement some functions of the MAClayer, and the MAC hardware processing unit 13 may implement theremaining functions of the MAC layer as hardware (hereinafter referredto as ‘MAC hardware’). However, embodiments of the MAC processor 11 arenot limited to this distribution of functionality.

The PHY processor 15 includes a transmitting (TX) signal processing unit100 and a receiving (RX) signal processing unit 200.

The baseband processor 10, the RF transceiver 20, the memory 40, theinput interface unit 50, and the output interface unit 60 maycommunicate with one another via the bus 70.

The RF transceiver 20 includes an RF transmitter 21 and an RF receiver22.

The memory 40 may further store an Operating System (OS) andapplications. The input interface unit 50 receives information from auser, and the output interface unit 60 outputs information to the user.

The antenna unit 30 includes one or more antennas. When Multiple InputMultiple Output (MIMO) or Multi-User MIMO (MU-MIMO) is used, the antennaunit 30 may include a plurality of antennas.

FIG. 2 is a schematic block diagram of an exemplary transmitting signalprocessor in a WLAN.

Referring to FIG. 2, the transmitting signal processing unit 100 mayinclude an encoder 110, an interleaver 120, a mapper 130, an InverseFourier Transformer (IFT) 140, and a Guard Interval (GI) inserter 150.

The encoder 110 encodes input data. For example, the encoder 100 may bea Forward Error Correction (FEC) encoder. The FEC encoder may include aBinary Convolutional Code (BCC) encoder followed by a puncturing device,or the FEC encoder may include a Low-Density Parity-Check (LDPC)encoder.

The transmitting signal processing unit 100 may further include ascrambler for scrambling the input data before encoding to reduce theprobability of long sequences of Os or ls. If BCC encoding is used inthe encoder 110, the transmitting signal processing unit 100 may furtherinclude an encoder parser for demultiplexing the scrambled bits among aplurality of BCC encoders. If LDPC encoding is used in the encoder 110,the transmitting signal processing unit 100 may not use the encoderparser.

The interleaver 120 interleaves the bits of each stream output from theencoder 110 to change the order of bits. Interleaving may be appliedwhen BCC encoding is used in the encoder 110. The mapper 130 maps thesequence of bits output from the interleaver 120 to constellationpoints. If LDPC encoding is used in the encoder 110, the mapper 130 mayfurther perform LDPC tone mapping in addition to constellation mapping.

When MIMO or MU-MIMO is used, the transmitting signal processing unit100 may use a plurality of interleavers 120 and a plurality of mappers130 corresponding to the number of spatial streams, NSS. In this case,the transmitting signal processing unit 100 may further include a streamparser for dividing outputs of the BCC encoders or output of the LDPCencoder into blocks that are sent to different interleavers 120 ormappers 130. The transmitting signal processing unit 100 may furtherinclude a Space-Time Block Code (STBC) encoder for spreading theconstellation points from the NSS spatial streams into NSTS space-timestreams and a spatial mapper for mapping the space-time streams totransmit chains. The spatial mapper may use direct mapping, spatialexpansion, or beamforming.

The IFT 140 converts a block of constellation points output from themapper 130 or the spatial mapper to a time-domain block (i.e., a symbol)by using Inverse Discrete Fourier Transform (IDFT) or Inverse FastFourier Transform (IFFT). If the STBC encoder and the spatial mapper areused, the IFT 140 may be provided for each transmit chain.

When MIMO or MU-MIMO is used, the transmitting signal processing unit100 may insert Cyclic Shift Diversities (CSDs) to prevent unintentionalbeamforming. The CSD insertion may occur before or after IFT. The CSDmay be specified per transmit chain or may be specified per space-timestream. Alternatively, the CSD may be applied as a part of the spatialmapper.

When MU-MIMO is used, some blocks before the spatial mapper may beprovided for each user.

The GI inserter 150 prepends a GI to the symbol. The transmitting signalprocessing unit 100 may optionally perform windowing to smooth edges ofeach symbol after inserting the GI. The RF transmitter 21 converts thesymbols into an RF signal and transmits the RF signal via the antennaunit 30. When MIMO or MU-MIMO is used, the GI inserter 150 and the RFtransmitter 21 may be provided for each transmit chain.

FIG. 3 is a schematic block diagram of an exemplary receiving signalprocessor in a WLAN.

Referring to FIG. 3, the receiving signal processing unit 200 includes aGI remover 220, a Fourier Transformer (FT) 230, a demapper 240, adeinterleaver 250, and a decoder 260.

An RF receiver 22 receives an RF signal via the antenna unit 30 andconverts the RF signal into one or more symbols. The GI remover 220removes the GI from the symbol. When MIMO or MU-MIMO is used, the RFreceiver 22 and the GI remover 220 may be provided for each receivechain.

The FT 230 converts the symbol (i.e., the time-domain block) into ablock of constellation points by using a Discrete Fourier Transform(DFT) or a Fast Fourier Transform (FFT). The FT 230 may be provided foreach receive chain.

When MIMO or MU-MIMO is used, the receiving signal processing unit 200may use/include a spatial demapper for converting Fourier Transformedreceiver chains to constellation points of the space-time streams, andan STBC decoder for despreading the constellation points from thespace-time streams into the spatial streams.

The demapper 240 demaps the constellation points output from the FT 230or the STBC decoder to bit streams. If LDPC encoding is applied to thereceived signal, the demapper 240 may further perform LDPC tonedemapping before constellation demapping. The deinterleaver 250deinterleaves the bits of each stream output from the demapper 240.Deinterleaving may be applied when a BCC encoding scheme is applied tothe received signal.

When MIMO or MU-MIMO is used, the receiving signal processing unit 200may use a plurality of demappers 240 and a plurality of deinterleavers250 corresponding to the number of spatial streams. In this case, thereceiving signal processing unit 200 may further include a streamdeparser for combining streams output from the deinterleavers 250.

The decoder 260 decodes the streams output from the deinterleaver 250 orthe stream deparser. For example, the decoder 100 may be an FEC decoder.The FEC decoder may include a BCC decoder or an LDPC decoder. Thereceiving signal processing unit 200 may further include a descramblerfor descrambling the decoded data. If BCC decoding is used in thedecoder 260, the receiving signal processing unit 200 may furtherinclude an encoder deparser for multiplexing the data decoded by aplurality of BCC decoders. If LDPC decoding is used in the decoder 260,the receiving signal processing unit 200 may not use the encoderdeparser.

In a WLAN system, Carrier Sense Multiple Access with Collision Avoidance(CSMA/CA) is a basic MAC access mechanism. The CSMA/CA mechanism isreferred to as Distributed Coordination Function (DCF) of IEEE 802.11MAC, or colloquially as a ‘listen before talk’ access mechanism.According to the CSMA/CA mechanism, an AP and/or a STA may sense amedium or a channel for a predetermined time before startingtransmission, that is, the AP and/or the STA may perform Clear ChannelAssessment (CCA). If the AP or the STA determines that the medium orchannel is idle, it may start to transmit a frame on the medium orchannel. On the other hand, if the AP and/or the STA determines that themedium or channel is occupied or busy, it may set a delay period (e.g.,a random backoff period), wait for the delay period without startingtransmission, and then attempt to transmit a frame. By applying a randombackoff period, a plurality of STAs are expected to attempt frametransmission after waiting for different time periods, resulting in lesscollisions.

FIG. 4 depicts a relationship between InterFrame Spaces (IFSs).

WLAN devices may exchange data frames, control frames, and managementframes with each other.

A data frame is used for transmission of data forwarded to a higherlayer. The WLAN device transmits the data frame after performing backoffif a Distributed Coordination Function IFS (DIFS) has elapsed from atime when the medium has been idle. A management frame is used forexchanging management information which is not forwarded to the higherlayer. The WLAN device transmits the management frame after performingbackoff if an IFS such as the DIFS or a Point Coordination Function IFS(PIFS) has elapsed. Subtype frames of the management frame include abeacon frame, an association request/response frame, a proberequest/response frame, and an authentication request/response frame. Acontrol frame is used for controlling access to the medium. Subtypeframes of the control frame include a Request-To-Send (RTS) frame, aClear-To-Send (CTS) frame, and an ACKnowledgement (ACK) frame. In thecase that the control frame is not a response frame to a previous frame,the WLAN device transmits the control frame after performing backoff ifthe DIFS has elapsed. In case that the control frame is a response frameto a previous frame, the WLAN device transmits the control frame withoutperforming backoff if a Short IFS (SIFS) has elapsed. The type andsubtype of a frame may be identified by a type field and a subtype fieldin a Frame Control (FC) field.

On the other hand, a Quality of Service (QoS) STA transmits a frameafter performing backoff if an Arbitration IFS (AIFS) for an associatedAccess Category (AC), i.e., AIFS [i] (i is determined based on AC) haselapsed. In this case, the AIFC [i] may be used for a data frame, amanagement frame, or a control frame that is not a response frame.

In the example illustrated in FIG. 4, upon generation of a frame to betransmitted, a STA may transmit the frame immediately, if it determinesthat the medium is idle for the DIFS or AIFS[i] or longer. The medium isbusy for a time period during which the STA transmits the frame. Duringthe time period, upon generation of a frame to be transmitted, anotherSTA may defer access by confirming that the medium is busy. If themedium is idle, the STA that intends to transmit the frame may perform abackoff operation after a predetermined IFS in order to minimizecollision with any other STA. Specifically, the STA that intends totransmit the frame selects a random backoff count, waits for a slot timecorresponding to the selected random backoff count, and then attemptstransmission. The random backoff count is determined based on aContention Window (CW) parameter and the medium is monitoredcontinuously during count-down of backoff slots (i.e. decrement abackoff count-down) according to the determined backoff count. If theSTA monitors the medium as busy, the STA discontinues the count-down andwaits, and then, if the medium gets idle, the STA resumes thecount-down. If the backoff slot count reaches 0, the STA may transmitthe next frame.

FIG. 5 is a conceptual diagram illustrating a CSMA/CA-based frametransmission procedure for avoiding collisions between frames in achannel.

Referring FIG. 5, a first STA (STA1) is a transmit WLAN device fortransmitting data, a second STA (STA2) is a receive WLAN device forreceiving the data from STA1, and a third STA (STA3) is a WLAN devicewhich may be located in an area where a frame transmitted from STA1and/or a frame transmitted from STA2 can be received by STA3.

STA1 may determine whether the channel is busy by carrier sensing. TheSTA1 may determine the channel occupation based on an energy level onthe channel or correlation of signals in the channel, or may determinethe channel occupation by using a Network Allocation Vector (NAV) timer.

After determining that the channel is not being used by other devicesduring DIFS (that is, the channel is idle), STA1 may transmit an RTSframe to STA2 after performing backoff Upon receiving the RTS frame,STA2 may transmit a CTS frame as a response to the CTS frame after SIFS.

When STA3 receives the RTS frame, STA3 may set the NAV timer for atransmission duration of subsequently transmitted frame by usingduration information included in the RTS frame. For example, the NAVtimer may be set for a duration of SIFS+ CTS frame duration+SIFS+ dataframe duration+SIFS+ACK frame duration. When STA3 receives the CTSframe, it may set the NAV timer for a transmission duration ofsubsequently transmitted frames by using duration information includedin the CTS frame. For example, the NAV timer may be set for a durationof SIFS+ a data frame duration+SIFS+an ACK frame duration. Uponreceiving a new frame before the NAV timer expires, STA3 may update theNAV timer by using duration information included in the new frame. STA3does not attempt to access the channel until the NAV timer expires.

When STA1 receives the CTS frame from STA2, it may transmit a data frameto STA2 after SIFS elapsed from the CTS frame has been completelyreceived. Upon successfully receiving the data frame, STA2 may transmitan ACK frame as a response to the data frame after SIFS elapsed.

When the NAV timer expires, STA3 may determine whether the channel isbusy through the use of carrier sensing. Upon determining that thechannel is not in use by other devices during DIFS and after the NAVtimer has expired, STA3 may attempt channel access after a contentionwindow after a random backoff has elapsed.

FIG. 6 depicts an exemplary frame structure in a WLAN system.

PHY layer may prepare for transmission of a MAC PDU (MPDU) in responseto an instruction (or a primitive, which is a set of instructions or aset of parameters) by the MAC layer. For example, upon receipt of aninstruction requesting transmission start from the MAC layer, the PHYlayer may switch to a transmission mode, construct a frame withinformation (e.g., data) received from the MAC layer, and transmit theframe.

Upon detection of a valid preamble in a received frame, the PHY layermonitors a header of the preamble and transmits an instructionindicating reception start of the PHY layer to the MAC layer.

Information is transmitted and received in frames in the WLAN system.For this purpose, a Physical layer Protocol Data Unit (PPDU) frameformat is defined.

A PPDU frame may include a Short Training Field (STF) field, a LongTraining Field (LTF) field, a SIGNAL (SIG) field, and a Data field. Themost basic (e.g., a non-High Throughput (non-HT)) PPDU frame may includeonly a Legacy-STF (L-STF) field, a Legacy-LTF (L-LTF) field, a SIGfield, and a Data field. Additional (or other types of) STF, LTF, andSIG fields may be included between the SIG field and the Data fieldaccording to the type of PPDU frame format (e.g., an HT-mixed formatPPDU, an HT-greenfield format PPDU, a Very High Throughput (VHT) PPDU,etc.).

The STF is used for signal detection, Automatic Gain Control (AGC),diversity selection, fine time synchronization, etc. The LTF field isused for channel estimation, frequency error estimation, etc. The STFand the LTF fields may be referred to as signals for OrthogonalFrequency Division Multiplexing (OFDM) PHY layer synchronization andchannel estimation.

The SIG field may include a RATE field and a LENGTH field. The RATEfield may include information about a modulation scheme and coding rateof data. The LENGTH field may include information about the length ofthe data. The SIG field may further include parity bits, SIG TAIL bits,etc.

The Data field may include a SERVICE field, a Physical layer ServiceData Unit (PSDU), and PPDU TAIL bits. When needed, the Data field mayfurther include padding bits. Some of the bits of the SERVICE field maybe used for synchronization at a descrambler of a receiver. The PSDUcorresponds to a MAC PDU defined at the MAC layer and may include datagenerated/used in a higher layer. The PPDU TAIL bits may be used toreturn an encoder to a zero state. The padding bits may be used to matchthe length of the Data filed in predetermined units.

A MAC PDU is defined according to various MAC frame formats. A basic MACframe includes a MAC header, a frame body, and a Frame Check Sequence(FCS). The MAC frame includes a MAC PDU and may be transmitted andreceived in the PSDU of the data part in the PPDU frame format.

The MAC header includes a Frame Control field, a Duration/Identifier(ID) field, an Address field, etc. The Frame Control field may includecontrol information required for frame transmission/reception. TheDuration/ID field may be set to a time for transmitting the frame. Fordetails of Sequence Control, QoS Control, and HT Control subfields ofthe MAC header, refer to the IEEE 802.11-2012 technical specification,which is hereby incorporated by reference.

The Frame Control field of the MAC header may include Protocol Version,Type, Subtype, To Distribution System (DS), From DS, More Fragment,Retry, Power Management, More Data, Protected Frame, and Ordersubfields. For the contents of each subfield in the Frame Control field,refer to the IEEE 802.11-2012 technical specification.

A Null-Data Packet (NDP) frame format is a frame format that does notinclude a data packet. In other words, the NDP frame format includes aPhysical Layer Convergence Protocol (PLCP) header part (i.e., the STF,LTF, and SIG fields) of the general PPDU frame format, without theremaining part (i.e., the Data field) of the general PPDU frame format.The NDP frame format may be referred to as a short frame format.

The IEEE 802.11ax task group is discussing a WLAN system, called a HighEfficiency WLAN (HEW) system, that operates in 2.4 GHz or 5 GHz andsupports a channel bandwidth (or channel width) of 20 MHz, 40 MHz, 80MHz, or 160 MHz. The present disclosure defines a new PPDU frame formatfor the IEEE 802.11ax HEW system. The new PPDU frame format may supportMU-MIMO or OFDMA. A PPDU of the new format may be referred to as a ‘HEWPPDU’ or ‘HE PPDU’ (similarly, HEW xyz may be referred to as ‘HE xyz’ or‘HE-xyz’ in the following descriptions).

In present disclosure, the term ‘MU-MIMO or OFDMA mode’ includes MU-MIMOwithout using OFDMA, or OFDMA mode without using MU-MIMO in anorthogonal frequency resource, or OFDMA mode using MU-MIMO in anorthogonal frequency resource.

FIG. 7 depicts an exemplary HE PPDU frame format.

A transmitting STA may generate a PPDU frame according to the HE PPDUframe format as illustrated in FIG. 7 and transmit the PPDU frame to areceiving STA. The receiving STA may receive, detect, and process thePPDU.

The HE PPDU frame format may broadly include two parts: the first partincluding an L-STF field, an L-LTF field, an L-SIG field, a RepeatedL-SIG (RL-SIG) field, a HE-SIG-A field, and a HE-SIG-B field and thesecond part including a HE-STF field, a HE-LTF field, and a HE-DATAfield. 64-FFT based on a channel bandwidth of 20 MHz may be applied tothe first part and a basic subcarrier spacing of 312.5 kHz and a basicDFT period of 3.2 μs may be included in the first part. 256-FFT based ona channel bandwidth of 20 MHz may be applied to the second part and abasic subcarrier spacing of 75.125kHz and a basic DFT period of 12.8 μsmay be included in the second part.

The HE-SIG-A field may include NHESIGA symbols, the HE-SIG-B field mayinclude NHESIGB symbols, the HE-LTF field may include NHELTF symbols,and the HE-DATA field may include NDATA symbols.

A detailed description of the fields included in the HE PPDU frameformat is given in Table I.

TABLE I DFT Subcarrier Element definition duration period GI spacingDescription Legacy(L)- Non-high 8 μs — — equivalent to L-STF of anon-trigger-based STF throughput(HT) 1,250 kHz PPDU has a periodicity of0.8 μs Short Training with 10 periods. field L-LTF Non-HT Long 8 μs 3.2μs 1.6 μs 312.5 kHz Training field L-SIG Non-HT 4 μs 3.2 μs 0.8 μs 312.5kHz SIGNAL field RL-SIG Repeated Non- 4 μs 3.2 μs 0.8 μs 312.5 kHz HTSIGNAL field HE-SIG-A HE SIGNAL A N_(HESIGA) * 3.2 μs 0.8 μs 312.5 kHzHE-SIG-A is duplicated on each field 4 μs 20 MHz segment after thelegacy preamble to indicate common control information. N_(HESIGA) meansthe number of OFDM symbols of the HE-SIG-A field and is equal to 2 or 4.HE-SIG-B HE SIGNAL B N_(HESIGB) * 3.2 μs 0.8 μs 312.5 kHz N_(HESIGB)means the number of field 4 μs OFDM symbols of the HE-SIG-B field and isvariable. DL MU packet contains HE-SIG-B. SU packets and UL Triggerbased packets do not contain HE-SIG-B. HE-STF HE Short 4 or 8 μs — —non- HE-STF of a non-trigger-based Training field trigger- PPDU has aperiodicity of 0.8 μs based with 5 periods. A non-trigger-based PPDU:PPDU is not sent in response to a (equivalent trigger frame. to) 1,250The HE-STF of a trigger-based kHz; PPDU has a periodicity of 1.6 μstrigger- with 5 periods. A trigger-based based PPDU is an UL PPDU sentin PPDU: response to a trigger frame. (equivalent to) 625 kHz HE-LTF HELong N_(HELTF) * 2xLTF: supports 2xLTF: HE PPDU shall support 2xLTFTraining field (DTF 6.4 μs 0.8, 1.6, (equivalent mode and 4xLTF mode.period + 4xLTF: 3.2 μs to) 156.25 In the 2xLTF mode, HE-LTF GI) μs 12.8μs kHz; symbol excluding GI is equivalent 4xLTF: to modulating everyother tone in 78.125 kHz an OFDM symbol of 12.8 μs excluding GI, andthen removing the second half of the OFDM symbol in time domain.N_(HELTF) means the number of HE-LTF symbols and is equal to 1, 2, 4, 6,8. HE-DATA HE DATA N_(DATA) * 12.8 μs supports 78.125 kHz N_(DATA) meansthe number of HE field (DTF 0.8, 1.6, data symbols. period + 3.2 μs GI)μs

L-STF is a non-HT Short Training field and may have a duration of 8 μsand a subcarrier spacing equivalent to 1250 kHz. L-STF of a PPDU whichis not based on a trigger may have a periodicity of 0.8 μs with 10periods. Herein, the trigger corresponds to scheduling information forUL transmission.

L-LTF is a non-HT Long Training field and may have a duration of 8 μs, aDFT period of 3.2 μs, a Guard Interval (GI) of 1.6 μs, and a subcarrierspacing of 312.5 kHz.

L-SIG is a non-HT SIGNAL field and may have a duration of 4 μs, a DFTperiod of 3.2 μs, a GI of 0.8 μs, and a subcarrier spacing of 312.5 kHz.

RL-SIG is a Repeated Non-HT SIGNAL field and may have a duration of 4μs, a DFT period of 3.2 μs, a GI of 0.8 μs, and a subcarrier spacing of312.5 kHz.

L-STF, L-LTF, L-SIG, and RL-SIG may be called legacy preambles.

HE-SIG-A is a HE SIGNAL A field and may have a duration of N_(HESIGA)*4μs, a DFT period of 3.2 μs, a GI of 0.8 μs, and a subcarrier spacing of312.5 kHz. HE-SIG-A may be duplicated on each 20 MHz segment after thelegacy preambles to indicate common control information. NHESIGArepresents the number of OFDM symbols of the HE-SIG-A field and may havea value of 2 or 4.

HE-SIG-B is a HE SIGNAL B field and may have a duration of N_(HESIGB)*4μs, a DFT period of 3.2 μs, a GI of 0.8 μs, and a subcarrier spacing of312.5 kHz. N_(HESIGB) represents the number of OFDM symbols of theHE-SIG-B field and may have a variable value. In addition, although a DLMulti-User (MU) packet may include the HE-SIG-B field, a Single-User(SU) packet and a UL trigger based packet may not include the HE-SIG-Bfield.

HE-STF is a HE Short Training field and may have a duration of 4 or 8μs. A non-trigger based PPDU may have a subcarrier spacing equivalent to1250 kHz and a trigger based PPDU may have a subcarrier spacingequivalent to 625 kHz. HE-STF of the non-triggered PPDU may have aperiodicity of 0.8 μs with 4 periods. The non-triggered PPDU is nottransmitted in response to a trigger field. HE-STF of the trigger basedPPDU may have a periodicity of 1.6 μs with 5 periods. The trigger basedPPDU is a UL PPDU transmitted in response to the trigger frame.

HE-LTF is a HE Long Training field and may have a duration ofN_(HELTF)*(DFT period+GI)μs. N_(HELTF) represents the number of HE-LTFsymbols and may have a value of 1, 2, 4, 6, or 8. A HE PPDU may supporta 2×LTF mode and a 4×LTF mode. In the 2×LTF mode, a HE-LTF symbol exceptfor a GI is equivalent to a symbol obtained by modulating every othertone in an OFDM symbol of 12.8 μs excluding a GI and then eliminatingthe first half or the second half of the OFDM symbol in the time domain.In the 4×LTF mode, a HE-LTF symbol excluding a GI are equivalent to asymbol obtained by modulating every fourth tone in an OFDM symbol of12.8 μs excluding a GI and then eliminating the first three-fourths orthe last three-fourths of the OFDM symbol in the time domain. 2×LTF mayhave a DFT period of 6.4 μs and 4×LTF may have a DFT period of 12.8 μs.A GI of HE-LTF may support 0.8 μs, 1.6 μs, and 3.2 μs. 2×LTF may have asubcarrier spacing equivalent to 156.25 kHz and 4×LTF may have asubcarrier spacing of 78.125 kHz.

HE-DATA is a HE DATA field and may have a duration of, NDATA*(DFTperiod+GI)μs. NDATA represents the number of HE-DATA symbols. HE-DATAmay have a DFT period of 12.8 μs. A GI of HE-DATA may support 0.8 μs,1.6 μs, and 3.2 μs. HE-DATA may have a subcarrier spacing of 78.125kHz.

The above description of the fields included in the HE PPDU frame formatmay be combined with exemplary HE PPDU frame formats described below.For example, characteristics of fields exemplarily described below maybe applied while a transmission order of the fields of the HE PPDU frameformat of FIG. 7 is maintained.

FIG. 8 depicts an exemplary HE PPDU frame format according to thepresent disclosure.

Referring to FIG. 8, the vertical axis represents frequency and thehorizontal axis represents time. It is assumed that frequency and timeincrease in the upward direction and the right direction, respectively.

In the example of FIG. 8, one channel includes four subchannels. AnL-STF, an L-LTF, an L-SIG, and a HE-SIG-A may be transmitted per channel(e.g., 20 MHz). A HE-STF and a HE-LTF may be transmitted on each basicsubchannel unit (e.g., 5 MHz)), and a HE-SIG-B and a PSDU may betransmitted on each of the subchannels allocated to a STA. A subchannelallocated to a STA may have a size required for PSDU transmission to theSTA. The size of the subchannel allocated to the STA may be N (N=1, 2, 3, . . .) times as large as the size of basic subchannel unit (i.e., asubchannel having a minimum size). In the example of FIG. 8, the size ofa subchannel allocated to each STA is equal to the size of the basicsubchannel unit. For example, a first subchannel may be allocated forPSDU transmission from an AP to STA1 and STA2, a second subchannel maybe allocated for PSDU transmission from the AP to STA3 and STA4, a thirdsubchannel may be allocated for PSDU transmission from the AP to STA5,and a fourth subchannel may be allocated for PSDU transmission from theAP to STA6.

While the term subchannel is used in the present disclosure, the termsubchannel may also be referred to as Resource Unit (RU) or subband. Inparticular, terms like OFDMA subchannel, OFDMA RU, OFDMA subband can beused as synonyms for OFDMA in the present disclosure. Terms like abandwidth of a subchannel, a number of tones (or subcarriers) allocatedto a subchannel, a number of data tones (or data subcarriers) allocatedto a subchannel can be used to express a size of a subchannel. Asubchannel refers to a frequency band allocated to a STA and a basicsubchannel unit refers to a basic unit used to represent the size of asubchannel. While the size of the basic subchannel unit is 5 MHz in theabove example, this is purely exemplary. Thus, the basic subchannel unitmay have a size of 2.5 MHz.

In FIG. 8, a plurality of HE-LTF elements are distinguished in the timeand frequency domains. One HE-LTF element may correspond to one OFDMsymbol in time domain and one subchannel unit (i.e., a subchannelbandwidth allocated to a STA) in frequency domain. The HE-LTF elementsare logical units, and the PHY layer does not necessarily operate inunits of a HE-LTF element. In the following description, a HE-LTFelement may be referred to shortly as a HE-LTF.

A HE-LTF symbol may correspond to a set of HE-LTF elements in one OFDMsymbol in time domain and in one channel unit (e.g., 20 MHz) infrequency domain.

A HE-LTF section may correspond to a set of HE-LTF elements in one ormore OFDM symbols in time domain and in one subchannel unit (i.e., asubchannel bandwidth allocated to a STA) in frequency domain.

A HE-LTF field may be a set of HE-LTF elements, HE-LTF symbols, orHE-LTF sections for a plurality of STAs.

The L-STF field is used for frequency offset estimation and phase offsetestimation, for preamble decoding at a legacy STA (i.e., a STA operatingin a system such as IEEE 802.11a/b/g/n/ac). The L-LTF field is used forchannel estimation, for the preamble decoding at the legacy STA. TheL-SIG field is used for the preamble decoding at the legacy STA andprovides a protection function for PPDU transmission of a third-partySTA (e.g., a third-party STA is not allowed to transmit during a certainperiod based on the value of a LENGTH field included in the L-SIGfield).

HE-SIG-A (or HEW SIG-A) represents High Efficiency Signal A (or HighEfficiency WLAN Signal A), and includes HE PPDU (or HEW PPDU) modulationparameters, etc. for HE preamble (or HEW preamble) decoding at a HE STA(or HEW STA). The set of parameters included in the HEW SIG-A field mayinclude one or more of Very High Throughput (VHT) PPDU modulationparameters transmitted by IEEE 802.11ac stations, as listed in Table IIbelow, to ensure backward compatibility with legacy STAs (e.g., IEEE802.11ac stations).

Two parts of Number VHT-SIG-A Bit Field of bits Description VHT-SIG-A1B0-B1 BW 2 Set to 0 for 20 MHz, 1 for 40 MHz, 2 for 80 MHz, and 3 for160 MHz and 80 + 80 MHz B2 Reserved 1 Reserved. Set to 1. B3 STBC 1 Fora VHT SU PPDU:  Set to 1 if space time block coding is used and set to 0 otherwise. For a VHT MU PPDU:  Set to 0. B4-B9 Group ID 6 Set to thevalue of the TXVECTOR parameter GROUP_ID. A value of 0 or 63 indicates aVHT SU PPDU; otherwise, indicates a VHT MU PPDU. B10-B21 NSTS/Partial 12For a VHT MU PPDU: NSTS is divided into 4 user AID positions of 3 bitseach. User position p, where 0 ≤ p ≤ 3, uses bits B(10 + 3p) to B(12 +3p). The number of space- time streams for user u are indicated at userposition p = USER_POSITION[u] where u = 0, 1, . . . , NUM_USERS − 1 andthe notation A[b] denotes the value of array A at index b. Zerospace-time streams are indicated at positions not listed in theUSER_POSITION array. Each user position is set as follows:  Set to 0 for0 space-time streams  Set to 1 for 1 space-time stream  Set to 2 for 2space-time streams  Set to 3 for 3 space-time streams  Set to 4 for 4space-time streams  Values 5-7 are reserved For a VHT SU PPDU: B10-B12 Set to 0 for 1 space-time stream  Set to 1 for 2 space-time streams Set to 2 for 3 space-time streams  Set to 3 for 4 space-time streams Set to 4 for 5 space-time streams  Set to 5 for 6 space-time streams Set to 6 for 7 space-time streams  Set to 7 for 8 space-time streamsB13-B21  Partial AID: Set to the value of the TXVECTOR  parameterPARTIAL_AID. Partial AID provides an  abbreviated indication of theintended recipient(s) of the  PSDU (see 9.17a). B22 TXOP_PS_NOT_ALLOWED1 Set to 0 by VHT AP if it allows non-AP VHT STAs in TXOP power savemode to enter Doze state during a TXOP. Set to 1 otherwise. The bit isreserved and set to 1 in VHT PPDUs transmitted by a non-AP VHT STA. B23Reserved 1 Set to 1 VHT-SIG-A2 B0 Short GI 1 Set to 0 if short guardinterval is not used in the Data field. Set to 1 if short guard intervalis used in the Data field. B1 Short GI 1 Set to 1 if short guardinterval is used and N_(SYM) mod 10 = 9; N_(SYM) otherwise, set to 0.N_(SYM) is defined in 22.4.3. Disambiguation B2 SU/MU[0] 1 For a VHT SUPPDU, B2 is set to 0 for BCC, 1 for LDPC Coding For a VHT MU PPDU, ifthe MU[0] NSTS field is nonzero, then B2 indicates the coding used foruser u with USER_POSITION[u] = 0; set to 0 for BCC and 1 for LDPC. Ifthe MU[0] NSTS field is 0, then this field is reserved and set to 1. B3LDPC Extra 1 Set to 1 if the LDPC PPDU encoding process (if an SU OFDMPPDU), or at least one LDPC user's PPDU encoding process Symbol (if aVHT MU PPDU), results in an extra OFDM symbol (or symbols) as describedin 22.3.10.5.4 and 22.3.10.5.5. Set to 0 otherwise. B4-B7 SU VHT- 4 Fora VHT SU PPDU: MCS/MU[1-3]  VHT-MCS index Coding For a VHT MU PPDU:  Ifthe MU[1] NSTS field is nonzero, then B4 indicates  coding for user uwith USER_POSITION[u] = 1: set to 0  for BCC, 1 for LDPC. If the MU[1]NSTS field is 0, then  B4 is reserved and set to 1.  If the MU[2] NSTSfield is nonzero, then B5 indicates  coding for user u withUSER_POSITION[u] = 2: set to 0  for BCC, 1 for LDPC. If the MU[2] NSTSfield is 0, then  B5 is reserved and set to 1.  If the MU[3] NSTS fieldis nonzero, then B6 indicates  coding for user u with USER_POSITION[u] =3: set to 0  for BCC, 1 for LDPC. If the MU[3] NSTS field is 0, then  B6is reserved and set to 1.  B7 is reserved and set to 1 B8 Beamformed 1For a VHT SU PPDU:  Set to 1 if a Beamforming steering matrix is appliedto the  waveform in an SU transmission as described in  20.3.11.11.2,set to 0 otherwise. For a VHT MU PPDU:  Reserved and set to 1 NOTE - Ifequal to 1 smoothing is not recommended. B9 Reserved 1 Reserved and setto 1 B10-B17 CRC 8 CRC calculated as in 20.3.9.4.4 with c7 in B10. Bits0-23 of HT-SIG1 and bits 0-9 of HT-SIG2 are replaced by bits 0-23 ofVHT-SIG-A1 and bits 0-9 of VHT-SIG-A2, respectively. B18-B23 Tail 6 Usedto terminate the trellis of the convolutional decoder. Set to 0.

Table II illustrates fields, bit positions, numbers of bits, anddescriptions included in each of two parts, VHT-SIG-A1 and VHT-SIG-A2,of the VHT-SIG-A field defined by the IEEE 802.11ac standard. Forexample, a BW (BandWidth) field occupies two Least Significant Bits(LSBs), B0 and B1 of the VHT-SIG-A1 field and has a size of 2 bits. Ifthe 2 bits are set to 0, 1, 2, or 3, the BW field indicates 20 MHz, 40MHz, 80 MHz, or 160 and 80+80 MHz. For details of the fields included inthe VHT-SIG-A field, refer to the IEEE 802.11ac-2013 technicalspecification, which is hereby incorporated by reference. In the HE PPDUframe format of the present disclosure, the HE-SIG-A field may includeone or more of the fields included in the VHT-SIG-A field, and it mayprovide backward compatibility with IEEE 802.11ac stations.

FIG. 9 depicts subchannel allocation in the HE PPDU frame formataccording to the present disclosure.

In FIG. 9, it is assumed that information indicating subchannelsallocated to STAs in HE PPDU indicates that 0 MHz subchannel isallocated to STA1 (i.e., no subchannel is allocated), a 5-MHz subchannelis allocated to each of STA2 and STA3, and a 10-MHz subchannel isallocated to STA4.

In the example of FIG. 9, an L-STF, an L-LTF, an L-SIG, and a HE-SIG-Amay be transmitted per channel (e.g., 20 MHz), a HE-STF and a HE-LTF maybe transmitted on each basic subchannel unit (e.g., 5 MHz), and aHE-SIG-B and a PSDU may be transmitted on each of the subchannelsallocated to STAs. A subchannel allocated to a STA has a size requiredfor PSDU transmission to the STA. The size of the subchannel allocatedto the STA may be an N (N=1, 2, 3 , . . . ) multiple of the size of thebasic subchannel unit (i.e., a minimum-size subchannel unit). In theexample of FIG. 9, the size of a subchannel allocated to STA2 is equalto that of the basic subchannel unit, the size of a subchannel allocatedto STA3 is equal to that of the basic subchannel unit, and the size of asubchannel allocated to STA4 is twice the size of the basic subchannelunit.

FIG. 9 illustrates a plurality of HE-LTF elements and a plurality ofHE-LTF subelements which are distinguished in the time and frequencydomains. One HE-LTF element may correspond to one OFDM symbol in thetime domain and one subchannel unit (i.e., the bandwidth of a subchannelallocated to a STA) in the frequency domain. One HE-LTF subelement maycorrespond to one OFDM symbol in the time domain and one basicsubchannel unit (e.g. 5 MHz) in the frequency domain. In the example ofFIG. 9, one HE-LTF element includes one HE-LTF subelement in the 5-MHzsubchannel allocated to STA2 or STA3. On the other hand, one HE-LTFelement includes two HE-LTF subelements in the third subchannel (i.e.,10-MHz subchannel, allocated to STA4). A HE-LTF element and a HE-LTFsubelement are logical units and the PHY layer does not always operatein units of a HE-LTF element or HE-LTF subelement.

A HE-LTF symbol may correspond to a set of HE-LTF elements in one OFDMsymbol in the time domain and one channel unit (e.g. 20 MHz) in thefrequency domain. That is, one HE-LTF symbol may be divided into HE-LTFelements by a subchannel width allocated to a STA and into HE-LTFsubelements by the width of the basic subchannel unit in the frequencydomain.

A HE-LTF section may correspond to a set of HE-LTF elements in one ormore OFDM symbols in the time domain and one subchannel unit (i.e. thebandwidth of a subchannel allocated to a STA) in the frequency domain. AHE-LTF subsection may correspond to a set of HE-LTF elements in one ormore OFDM symbols in the time domain and one basic subchannel unit(e.g., 5 MHz) in the frequency domain. In the example of FIG. 9, oneHE-LTF section includes one HE-LTF subsection in the 5-MHz subchannelallocated to STA2 or STA3. On the other hand, one HE-LTF sectionincludes two HE-LTF subsections in the third subchannel (i.e., 10-MHzsubchannel, allocated to STA4).

A HE-LTF field may correspond to a set of HE-LTF elements (orsubelements), HE-LTF symbols, or HE-LTF sections (or subsections) for aplurality of STAs.

For the afore-described HE PPDU transmission, subchannels allocated to aplurality of HE STAs may be contiguous in the frequency domain. In otherwords, for HE PPDU transmission, the subchannels allocated to the HESTAs may be sequential and any intermediate one of the subchannels ofone channel (e.g., 20 MHz) may not be allowed to be unallocated orempty. Referring to FIG. 8, if one channel includes four subchannels, itmay not be allowed to keep the third subchannel unallocated and empty,while the first, second, and fourth subchannels are allocated to STAs.However, the present disclosure does not exclude non-allocation of anintermediate subchannel of one channel to a STA.

FIG. 10 depicts a subchannel allocation method according to the presentdisclosure.

In the example of FIG. 10, a plurality of contiguous channels (e.g.,20-MHz-bandwidth channels) and boundaries of the plurality of contiguouschannels are shown. In FIG. 10, a preamble may correspond to an L-STF,an L-LTF, an L-SIG, and a HE-SIG-A as illustrated in the examples ofFIGS. 8 and 9.

A subchannel for each HE STA may be allocated within one channel, andmay not be allocated with partially overlapping between a plurality ofchannels. That is, if there are two contiguous 20-MHz channels CH1 andCH2, subchannels for STAs paired for MU-MIMO-mode or OFDMA-modetransmission may be allocated either within CH1 or within CH2, and itmay be prohibited that one part of a subchannel exists in CH1 andanother part of the subchannel exists in CH2. This means that onesubchannel may not be allocated with crossing a channel boundary. Fromthe perspective of RUs supporting the MU-MIMO or OFDMA mode, a bandwidthof 20 MHz may be divided into one or more RUs, and a bandwidth of 40 MHzmay be divided into one or more RUs in each of two contiguous 20-MHzbandwidths, and no RU is allocated with crossing the boundary betweentwo contiguous 20-MHz bandwidths.

As described above, it is not allowed that one subchannel belongs to twoor more 20-MHz channels. Particularly, a 2.4-GHz OFDMA mode may supporta 20-MHz OFDMA mode and a 40-MHz OFDMA mode. In the 2.4-GHz OFDMA mode,it may not be allowed that one subchannel belongs to two or more 20-MHzchannels.

FIG. 10 is based on the assumption that subchannels each having the sizeof a basic subchannel unit (e.g., 5 MHz) in CH1 and CH2 are allocated toSTA1 to STA7, and subchannels, each having double the size (e.g., 10MHz) of the basic subchannel unit in CH4 and CHS, are allocated to STA8,STA9, and STA10.

As illustrated in the lower part of FIG. 10, although a subchannelallocated to STA1, STA2, STA3, STA5, STA6, or STA7 is fully overlappedonly with one channel (i.e., without crossing the channel boundary, orbelonging only to one channel), a subchannel allocated to STA4 ispartially overlapped with the two channels (i.e., crossing the channelboundary, or belonging to two channels). In the foregoing example of thepresent disclosure, the subchannel allocation to STA4 is not allowed.

As illustrated in the upper part of FIG. 10, although a subchannelallocated to STA8 or STA10 is fully overlapped only with one channel(i.e., without crossing the channel boundary, or belonging only to onechannel), a subchannel allocated to STA9 is partially overlapped withtwo channels (i.e., crossing the channel boundary, or belonging to twochannels). In the foregoing example of the present disclosure, thesubchannel allocation to STA9 is not allowed.

On the other hand, in some embodiments, it may be allowed to allocate asubchannel partially overlapped between a plurality of channels (i.e.,crossing the channel boundary, or belonging to two or more channels).For example, in SU-MIMO mode transmission, a plurality of contiguouschannels may be allocated to a STA and any of one or more subchannelsallocated to the STA may cross the boundary between two contiguouschannels.

While the following description is given with an assumption that onesubchannel has a channel bandwidth of 5 MHz in one channel having achannel bandwidth of 20 MHz, this is provided to simplify thedescription of the principle of the present disclosure and thus shouldnot be construed as limiting the present disclosure. For example, thebandwidths of a channel and a subchannel may be defined or allocated asvalues other than the above examples. In addition, a plurality ofsubchannels in one channel may have the same or different channelwidths.

FIG. 11 depicts the starting and ending points of a HE-LTF field in theHE PPDU frame format according to the present disclosure.

To support the MU-MIMO mode and the OFDMA mode, the HE PPDU frame formataccording to the present disclosure may include, in the HE-SIG-A field,information about the number of spatial streams to be transmitted to aHE STA allocated to each subchannel.

If MU-MIMO-mode or OFDMA-mode transmission is performed to a pluralityof HE STAs on one subchannel, the number of spatial streams to betransmitted to each of the HE STAs may be provided in the HE-SIG-A orHE-SIG-B field, which will be described later in additional detail.

FIG. 11 is based on the assumption that a first 5-MHz subchannel isallocated to STA1 and STA2 and two spatial streams are transmitted toeach STA in a DL MU-MIMO or OFDMA mode (i.e., a total of four spatialstreams are transmitted on one subchannel). For this purpose, a HE-STF,a HE-LTF, a HE-LTF, a HE-LTF, a HE-LTF, and a HE-SIG-B follow theHE-SIG-A field on the subchannel. The HE-STF is used for frequencyoffset estimation and phase offset estimation for the 5-MHz subchannel.The HE-LTFs are used for channel estimation for the 5-MHz subchannel.Since the subchannel carries four spatial streams, as many HE-LTFs(i.e., HE-LTF symbols or HE-LTF elements in a HE-LTF section) as thenumber of the spatial streams, that is, four HE-LTFs are transmitted tosupport MU-MIMO transmission.

According to an example of the present disclosure, the relationshipbetween a total number of spatial streams transmitted on one subchanneland a number of HE-LTFs is listed in Table III.

Total number of spatial streams transmitted on one subchannel Number ofHE-LTFs 1 1 2 2 3 4 4 4 5 6 6 6 7 8 8 8

Referring to Table III as an example, if one spatial stream istransmitted on one subchannel, at least one HE-LTF needs to betransmitted on the subchannel. If an even number of spatial streams aretransmitted on one subchannel, at least as many HE-LTFs as the number ofthe spatial streams need to be transmitted. If an odd number of spatialstreams greater than one are transmitted on one subchannel, at least asmany HE-LTFs as a number that is 1 larger than the number of the spatialstreams need to be transmitted.

Referring to FIG. 11 again, it is assumed that the second 5-MHzsubchannel is allocated to STA3 and STA4 and one spatial stream per STAis transmitted in the DL MU-MIMO or OFDMA mode (i.e., a total of twospatial streams are transmitted on one subchannel). In this case, twoHE-LTFs need to be transmitted on the second subchannel, however, in theexample of FIG. 11, a HE-STF, a HE-LTF, a HE-LTF, a HE-LTF, a HE-LTF,and a HE-SIG-B follow the HE-SIG-A field on the subchannel (i.e., fourHE-LTFs are transmitted). This is for the purpose of setting the samestarting time of PSDU transmission for subchannels allocated to otherSTAs paired with STA3 and STA4 for MU-MIMO transmission. If only twoHE-LTFs are transmitted on the second subchannel, PSDUs are transmittedat different time points on the first and second subchannels. PSDUtransmission on each subchannel at a different time point results indiscrepancy between OFDM symbol timings of subchannels, therebydisrupting orthogonality (i.e., orthogonality is not maintained). Toovercome this problem, an additional constraint needs to be imposed forHE-LTF transmission.

Basically, transmission of as many HE-LTFs as required is sufficient inan SU-MIMO or non-OFDMA mode. However, timing synchronization (oralignment) with fields transmitted on subchannels for other paired STAsis required in the MU-MIMO or OFDMA mode. Accordingly, the number ofHE-LTFs may be determined for all other subchannels based on asubchannel having the maximum number of streams in MU-MIMO-mode orOFDMA-mode transmission.

Specifically, the numbers of HE-LTFs may be determined for allsubchannels according to the maximum of the number of HE-LTFs (HE-LTFsymbols or HE-LTF elements in a HE-LTF section) required according tothe total number of spatial streams transmitted on each subchannel, fora set of HE STAs allocated to each subchannel. A “set of HE STAsallocated to each subchannel” is one HE STA in the SU-MIMO mode, and aset of HE STAs paired across a plurality of subchannels in the MU-MIMOmode. The ‘number of spatial streams transmitted on each subchannel’ isthe number of spatial streams transmitted to one HE STA in the SU-MIMOmode, and the number of spatial streams transmitted to a plurality of HESTAs paired on the subchannel in the MU-MIMO mode.

That is, it may be said that a HE-LTF field starts at the same timepoint and ends at the same time point in a HE PPDU for all users (i.e.HE STAs) in MU-MIMO-mode or OFDMA-mode transmission. Or it may be saidthat the lengths of HE-LTF sections are equal on a plurality ofsubchannels for all users (i.e. HE STAs) in MU-MIMO-mode or OFDMA-modetransmission. Or it may be said that the number of HE-LTF elementsincluded in each HE-LTF section is equal on a plurality of subchannelsfor all users (i.e. HE STAs) in MU-MIMO-mode or OFDMA-mode transmission.Accordingly, PSDU transmission timings may be synchronized among aplurality of subchannels for all HE STAs in MU-MIMO-mode or OFDMA-modetransmission.

As described above, the number of HE-LTF symbols (refer to FIG. 8) maybe 1, 2, 4, 6, or 8 in HE PPDU transmission in the MU-MIMO or OFDMAmode, determined according to the maximum of the numbers of spatialstreams on each of a plurality of subchannels. A different number ofspatial streams may be allocated to each of a plurality of subchannels,and the number of spatial streams allocated to one subchannel is thenumber of total spatial streams for all users allocated to thesubchannel. That is, the number of HE-LTF symbols may be determinedaccording to the number of spatial streams allocated to a subchannelhaving a maximum number of spatial streams by comparing the number oftotal spatial streams for all users allocated to one of a plurality ofsubchannels with the number of total spatial streams for all usersallocated to another subchannel.

Specifically, in HE PPDU transmission in the OFDMA mode, the number ofHE-LTF symbols may be 1, 2, 4, 6, or 8, determined based on the numberof spatial streams transmitted in a subchannel having a maximum numberof spatial streams across a plurality of subchannels. Further, in HEPPDU transmission in the OFDMA mode, the number of HE-LTF symbols may bedetermined based on whether the number of spatial streams transmitted ina subchannel having a maximum number of spatial streams across aplurality of subchannels is odd or even (refer to Table III). That is,in HE PPDU transmission in the OFDMA mode, when the number (e.g., K) ofspatial streams transmitted in a subchannel having a maximum number ofspatial streams across a plurality of subchannels is an even number, thenumber of HE-LTF symbols may be equal to K. In HE PPDU transmission inthe OFDMA mode, when the number, K, of spatial streams transmitted in asubchannel having a maximum number of spatial streams across a pluralityof subchannels is an odd number greater than one, the number of HE-LTFsymbols may be equal to K+1.

When only one STA is allocated to one subchannel in OFDMA mode (i.e.,OFDMA mode without using MU-MIMO), a subchannel having a maximum numberof spatial streams across a plurality of subchannels may be determinedby the number of spatial streams for a STA allocated to each subchannel.When more than one STA is allocated to one subchannel in OFDMA mode(i.e., OFDMA mode using MU-MIMO), a subchannel having a maximum numberof spatial streams across a plurality of subchannels may be determinedby the number of STAs allocated to each subchannel and the number ofspatial streams for each STA allocated to each subchannel (e.g., if STA1and STA2 are allocated to one subchannel, sum of the number of spatialstreams for STA1 and the number of spatial streams for STA2).

When transmitting a HE PPDU frame in the MU-MIMO or OFDMA mode, atransmitter may generate P (where P is an integer equal to or largerthan 1) HE-LTF symbols (refer to FIG. 8) and transmit a HE PPDU frameincluding at least the P HE-LTF symbols and a Data field to a receiver.The HE PPDU frame may be divided into Q subchannels in the frequencydomain (Q is an integer equal to or larger than 2). Each of the P HE-LTFsymbols may be divided into Q HE-LTF elements corresponding to the Qsubchannels in the frequency domain. That is, the HE PPDU may include PHE-LTF elements on one subchannel (herein, the P HE-LTF elements maybelong to one HE-LTF section on the subchannel).

As described above, the number of HE-LTF elements (i.e., P) in one ofthe Q subchannels may be equal to the number of HE-LTF elements (i.e.,P) of another subchannel. Also, the number of HE-LTF elements (i.e., P)included in a HE-LTF section in one of the Q subchannels may be equal tothe number of HE-LTF elements (i.e., P) included in a HE-LTF section inanother subchannel. The HE-LTF section of one of the Q subchannels maystart and end at the same time points as the HE-LTF section of anothersubchannel. Also, the HE-LTF sections may start and end at the same timepoints across the Q subchannels (i.e., across all users or STAs).

Referring to FIG. 11 again, the third 5-MHz subchannel is allocated toSTA5 and one spatial stream is transmitted on the subchannel in SU-MIMO(considering all subchannels, a plurality of spatial streams aretransmitted to STA1 to STA6 in MU-MIMO or OFDMA mode). In this case,although transmission of one HE-LTF is sufficient for the subchannel, asmany HE-LTFs as the maximum of the numbers of HE-LTFs on the othersubchannels, that is, four HE-LTFs are transmitted on the subchannel inorder to align the starting points and ending points of the HE-LTFfields of the subchannels.

The fourth 5-MHz subchannel is allocated to STA6 and one spatial streamis transmitted on the subchannel in SU-MIMO (considering all othersubchannels, a plurality of spatial streams are transmitted to STA1 toSTA6 in MU-MIMO or OFDMA mode). In this case, although transmission ofone HE-LTF is sufficient for the subchannel, as many HE-LTFs as themaximum of the numbers of HE-LTFs on the other subchannels, that is,four HE-LTFs are transmitted on the subchannel in order to align thestarting points and ending points of the HE-LTF fields of thesubchannels.

In the example of FIG. 11, the remaining two HE-LTFs except two HE-LTFsrequired for channel estimation of STA3 and STA4 on the secondsubchannel, the remaining three HE-LTFs except one HE-LTF required forchannel estimation of STA5 on the third subchannel, and the remainingthree HE-LTFs except one HE-LTF required for channel estimation of STA6on the fourth subchannel may be said to be placeholders that are notactually used for channel estimation at the STAs.

FIG. 12 depicts a HE-SIG-B field and a HE-SIG-C field in the HE PPDUframe format according to the present disclosure.

To effectively support MU-MIMO-mode or OFDMA-mode transmission in the HEPPDU frame format according to the present disclosure, independentsignaling information may be transmitted on each subchannel.Specifically, a different number of spatial streams may be transmittedto each of a plurality of HE STAs that receive an MU-MIMO-mode orOFDMA-mode transmission simultaneously. Therefore, information about thenumber of spatial streams to be transmitted should be indicated to eachHE STA.

Information about the number of spatial streams on one channel may beincluded in, for example, a HE-SIG-A field. A HE-SIG-B field may includespatial stream allocation information about one subchannel. Also, aHE-SIG-C field may be transmitted after transmission of HE-LTFs,including Modulation and Coding Scheme (MCS) information about a PSDUand information about the length of the PSDU, etc.

FIG. 13 depicts OFDM symbol durations and GI lengths in the HE PPDUframe format according to the present disclosure.

In the HE PPDU frame format according to the present disclosure, L-STF,L-LTF, L-SIG, and HE-SIG-A fields may be configured with 4.0-μs OFDMsymbols based on 64-FFT. One OFDM symbol has a GI of 0.8 μs. In thepresent disclosure, a GI value applied to the L-STF, L-LTF, L-SIG, andHE-SIG-A fields is defined as G1. The L-STF, L-LTF, L-SIG, and HE-SIG-Afields may include 3.2-μs OFDM symbols based on 64-FFT, excluding theGIs. The term 64 FFT-based symbol is used mainly based on a channelbandwidth of 20 MHz. If the term 64 FFT-based symbol is usedirrespective of a channel bandwidth, a 64 FFT-based symbol may mean asymbol having a symbol duration of 3.2 μs and a subcarrier spacing of312.5 kHz.

The following HE-STF, HE-LTF, HE-SIG-B, and PSDU fields may include16-μs OFDM symbols based on 256-FFT. The OFDM symbol duration may bechanged according to a GI value. Two types of GI values may be definedfor one OFDM symbol during different time periods. A GI value applied tothe OFDM symbols of the HE-STF, HE-LTF, and HE-SIG-B fields is definedas G2 and a GI value applied to the OFDM symbols of the PSDU is definedas G3. Excluding the GIs, the HE-STF, HE-LTF, HE-SIG-B, and PSDU fieldsmay be configured with 12.8-μs OFDM symbols based on 256-FFT. The term256 FFT-based symbol is used mainly based on a channel bandwidth of 20MHz. If the term 256 FFT-based symbol is used irrespective of a channelbandwidth, a 256 FFT-based symbol may mean a symbol having a symbolduration of 12.8-μs and a subcarrier spacing of 78.125 kHz.

The values of G2 and G3 may be equal or different. If G2 and G3 areequal, G2 and G3 may be defined as one parameter without distinguishingbetween G2 and G3. In one embodiment, unlike G1, G2 and G3 may varyaccording to a transmitted PPDU transmission vector, rather than beingfixed values (i.e., predetermined values). This is because the lengthsof the HE-STF, HE-LTF, and HE-SIG-B fields to which G2 is applied mayvary according to a PPDU transmission vector and the length of the PSDUto which G3 is applied may also vary according to the PPDU transmissionvector.

For example, G1 may have a fixed value (i.e., a predetermined value) of0.8,μs, G2 may be a value selected from 3.2 μs, 1.6 μs, 0.8 μs, and 0.4μs, and G3 may be a value selected from among 3.2 μs, 1.6 μs, 0.8 μs,and 0.4 μs. Also, G1 may have a fixed value (i.e., a predeterminedvalue) of 0.8 μs, and G2 or G3 may be a value selected or determinedfrom among 3.2 μs, 1.6 μs, 0.8 μs, and 0.4 μs. In one embodiment, G1does not require separate signaling because G1 is a fixed value, andsignaling information indicating G2 and G3 may be provided to a HE STAin the HE-SIG-A field.

In one embodiment, G2 and G3 are applied commonly across all OFDMsymbols transmitted during a corresponding time period and across allsubchannels. Accordingly, PSDU transmission timings and OFDM symboltimings may be synchronized. For example, it may not be allowed to applya 3.2-μs G2 value to a subchannel and a 1.6-μs or 0.8-μs G2 value toanother subchannel during a specific time period. Rather, the same3.2-μs G2 value may be applied to the subchannels during the same timeperiod. In a similar example, it may not be allowed to apply a 1.6-μs G3value to a subchannel and a 3.2-μs or 0.8-μs G3 value to anothersubchannel during a specific time period. Rather, the same 1.6-μs G3value may be applied to the subchannels during the same time period.

In the case where a HE PPDU frame format having HE-LTF sections ofdifferent lengths for subchannels is used (i.e., in the case where thenumber of HE-LTFs is not determined for each subchannel based on themaximum of the number of HE-LTFs required according to the total numberof spatial streams transmitted on each subchannel in a set of HE STAsallocated to each of subchannels, as described in the example of FIG.11), if the values of G2 and G3 are different, PSDUs are transmitted ondifferent subchannels at different time points and OFDM symbol timingsare not synchronized. Therefore, values of G2 and G3 may need to beselected or determined as a same value.

In the case where a HE PPDU frame format having HE-LTF sections of thesame length for subchannels is used (i.e., in the case where the numberof HE-LTFs is determined for each subchannel based on the maximum of thenumbers of HE-LTFs required according to the total number of spatialstreams transmitted on each subchannel in a set of HE STAs allocated toeach of subchannels, as described in the example of FIG. 11), eventhough the values of G2 and G3 are different, PSDUs are transmitted onthe subchannels at the same time point, without causing discrepancybetween OFDM symbol timings. Therefore, values of G2 and G3 may beselected or determined as different values. However, even in this case,the present disclosure does not exclude that values of G2 and G3 may beselected or determined as a same value.

In the example of FIG. 13, OFDM symbol durations S1, S2, and S3 may beapplied respectively to time periods to which the GIs G1, G2, and G3 areapplied.

FIG. 14 depicts an exemplary HE PPDU frame format for a wide channelband according to the present disclosure.

Referring to FIG. 14, the HE PPDU frame format for one 20-MHz channelillustrated in the example of FIG. 13 is extended to two 20-MHzchannels. Similarly, HE PPDU frame formats for the channel bandwidths of80 MHz and 160 MHz may be configured by extending the HE PPDU frameformat for one 20-MHz channel illustrated in the example of FIG. 13 tofour and eight 20-MHz channels, respectively.

There is no modification involved in extending the HE PPDU frame formatfor one 20-MHz channel. In other words, all subchannels across one ormore 20-MHz channels are the same in terms of PSDU transmission timepoints, OFDM symbol durations, and GIs.

From this viewpoint, the example described with reference to FIG. 11 inwhich “the lengths of HE-LTF sections across subchannels are equal” maybe extended to simultaneous application on a channel basis as well as ona subchannel basis. Therefore, PSDU transmission timings and OFDM symboltimings are synchronized for users paired for MU-MIMO-mode or OFDMA-modetransmission, thus maintaining orthogonality. This channel-based examplewill be described below.

Basically in SU-MIMO-mode or non-OFDMA-mode transmission, it issufficient to transmit as many HE-LTFs as required. However, the timingsof fields transmitted on subchannels for other paired STAs need to besynchronized (or aligned) across all subchannels over one or more 20-MHzchannels in MU-MIMO-mode or OFDMA-mode transmission. Therefore, thenumbers of HE-LTFs on all other subchannels over one or more 20-MHzchannels may be determined based on a subchannel having a maximum numberof streams among all subchannels over one or more 20-MHz channels inMU-MIMO-mode or OFDMA-mode transmission.

Specifically, the number of HE-LTFs to be transmitted on all subchannelsmay be determined according to the maximum of the number of HE-LTFsrequired according to the total numbers of spatial streams transmittedon each subchannel over one or more 20-MHz channels, for a set of HESTAs allocated to each of the subchannels. Herein, ‘the set of HE STAsallocated to each of the subchannels over one or more 20-MHz channels’is one HE STA in the SU-MIMO mode, whereas it is a set of a plurality ofHE STAs paired on all subchannels over one or more 20-MHz channels inthe MU-MIMO mode or OFDMA mode. The ‘total number of spatial streamstransmitted on each of all subchannels over one or more 20-MHz channels’is the number of spatial streams transmitted to one HE STA in theSU-MIMO mode and the number of spatial streams transmitted to aplurality of HE STAs paired on the subchannel in the MU-MIMO mode orOFDMA mode.

That is, it may be said that a HE-LTF field starts at the same timepoint and ends at the same time point on all subchannels over one ormore 20-MHz channels for all users (i.e., HE STAs) in MU-MIMO-mode orOFDMA-mode transmission of a HE PPDU. Or it may be said that the lengthsof HE-LTF sections are equal on all subchannels over one or more 20-MHzchannels for all HE STAs in MU-MIMO-mode or OFDMA-mode transmission. Orit may be said that the number of HE-LTF elements included in eachHE-LTF section is equal in all subchannels over one or more 20-MHzchannels for all HE STAs in MU-MIMO-mode or OFDMA-mode transmission.Accordingly, PSDU transmission timings may be synchronized between allsubchannels over one or more 20-MHz channels for all HE STAs inMU-MIMO-mode or OFDMA-mode transmission.

In FIG. 14, the OFDM symbol duration and GI of L-STF, L-LTF, L-SIG, andHE-SIG-A fields on the first 20-MHz channel are S1 and G1, respectively.Like the first 20-MHz channel, the second 20-MHz channel has S1 and G1respectively as the OFDM symbol duration and GI of L-STF, L-LTF, L-SIG,and HE-SIG-A fields.

In FIG. 14, the OFDM symbol duration and GI of a HE-STF field, aplurality of HE-LTFs, and a HE-SIG-B field on the first 20-MHz channelare S2 and G2, respectively. Like the first 20-MHz channel, the OFDMsymbol duration and GI of a HE-STF field, a plurality of HE-LTFs, and aHE-SIG-B field on the second 20-MHz channel are also S2 and G2,respectively.

In FIG. 14, the OFDM symbol duration and GI of a PSDU on the first20-MHz channel are S3 and G3, respectively. Like the first 20-MHzchannel, the OFDM symbol duration and GI of a PSDU on the second 20-MHzchannel are also S3 and G3, respectively.

This example it is shown that if the OFDM symbol duration and GI of one20-MHz channel are determined based on 64-FFT, the OFDM symbol durationand GI of the other 20-MHz channel(s) should be determined based on64-FFT. In other words, if the OFDM symbol duration and GI of one 20-MHzchannel are determined based on 64-FFT, the OFDM symbol duration and GIof the other 20-MHz channel(s) should not be determined based on256-FFT.

In a modified example, although subchannels within one 20-MHz channelmay have the same OFDM symbol durations and the same GIs, subchannelswithin another 20-MHz channel may have different OFDM symbol durationsand GIs. For example, while S2, G2, S3, and G3 are applied as OFDMsymbol durations and GIs for subchannels within the first 20-MHzchannel, different values (e.g., S4, G4, S5, and G5) may be applied asOFDM symbol durations and GIs for subchannels within the second 20-MHzchannel. Even in this case, the OFDM symbol duration and GI, S1 and G1,applied to L-STF, L-LTF, and L-SIG fields in a different 20-MHz channelmay be the same fixed values in every 20-MHz channel.

Further, this modified example may include application of the exampledescribed before with reference to FIG. 11 in which subchannels have thesame HE-LTF section length' only to subchannels within one 20-MHzchannel, not to the HE-LTF section length of subchannels in another20-MHz channel.

With reference to the foregoing examples of the present disclosure,mainly the features of a HE PPDU frame structure applicable to a DLMU-MIMO-mode or OFDMA-mode transmission that an AP transmitssimultaneously to a plurality of STAs has been described. Now, adescription will be given of the features of a HE PPDU frame structureapplicable to a UL MU-MIMO-mode or OFDMA-mode transmission that aplurality of STAs transmit simultaneously to an AP.

The above-described various examples of structures of the HE PPDU frameformat supporting MU-MIMO-mode or OFDMA-mode transmission should not beunderstood as applicable only to DL without being applicable to UL.Rather, the examples should be understood as also applicable to UL. Forexample, the above-described exemplary HE PPDU frame formats may also beused for a UL HE PPDU transmission that a plurality of STAssimultaneously transmit to a single AP.

However, in the case of a DL MU-MIMO-mode or OFDMA-mode HE PPDUtransmission that an AP simultaneously transmits to a plurality of STAs,the transmission entity, AP has knowledge of the number of spatialstreams transmitted to a HE STA allocated to each of a plurality ofsubchannels. Therefore, the AP may include, in a HE-SIG-A field or aHE-SIG-B field, information about the total number of spatial streamstransmitted across a channel, a maximum number of spatial streams (i.e.,information being a basis of the number of HE-LTF elements (or thestarting point and ending point of a HE-LTF section) on eachsubchannel), and the number of spatial streams transmitted on eachsubchannel. In contrast, in the case of a UL MU-MIMO-mode or OFDMA-modeHE PPDU transmission that a plurality of STAs simultaneously transmit toan AP, each STA being a transmission entity may only be aware of thenumber of spatial streams in a HE PSDU that it will transmit, withoutknowledge of the number of spatial streams in a HE PSDU transmitted byanother STA paired with the STA. Accordingly, the STA may determineneither the total number of spatial streams transmitted across a channelnor a maximum number of spatial streams.

To solve this problem, a common parameter (i.e., a parameter appliedcommonly to STAs) and an individual parameter (a separate parameterapplied to an individual STA) may be configured as follows in relationto a UL HE PPDU transmission.

For simultaneous UL HE PPDU transmissions from a plurality of STAs to anAP, a protocol may be designed in such a manner that the AP sets acommon parameter or individual parameters (common/individual parameters)for the STAs for the UL HE PPDU transmissions and each STA operatesaccording to the common/individual parameters. For example, the AP maytransmit a trigger frame (or polling frame) for a UL MU-MIMO-mode orOFDMA-mode transmission to a plurality of STAs. The trigger frame mayinclude a common parameter (e.g., the number of spatial streams across achannel or a maximum number of spatial streams) and individualparameters (e.g., the number of spatial streams allocated to eachsubchannel), for the UL MU-MIMO-mode or OFDMA-mode transmission. As aconsequence, a HE PPDU frame format applicable to a UL MU-MIMO or OFDMAmode may be configured without modification to an exemplary HE PPDUframe format applied to a DL MU-MIMO or OFDMA mode. For example, eachSTA may configure a HE PPDU frame format by including information aboutthe number of spatial streams across a channel in a HE-SIG-A field,determining the number of HE-LTF elements (or the starting point andending point of a HE-LTE section) on each subchannel according to themaximum number of spatial streams, and including information about thenumber of spatial streams for the individual STA in a HE-SIG-B field.

Alternatively, if the STAs operate according to the common/individualparameters received in the trigger frame from the AP, each STA does notneed to indicate the common/individual parameters to the AP during a HEPPDU transmission. Therefore, this information may not be included in aHE PPDU. For example, each STA may determine the total number of spatialstreams, the maximum number of spatial streams, and the number ofspatial streams allocated to individual STA, as indicated by the AP, andconfigure a HE PPDU according to the determined numbers, withoutincluding information about the total number of spatial streams or thenumber of spatial streams allocated to the STA in the HE PPDU.

On the other hand, if the AP does not provide common/individualparameters in a trigger frame, for a UL MIMO-mode or OFDMA-mode HE PPDUtransmission, the following operation may be performed.

Common transmission parameters (e.g., channel BandWidth (BW)information, etc.) for simultaneously transmitted HE PSDUs may beincluded in HE-SIG-A field, but parameters that may be different forindividual STAs (e.g., the number of spatial streams, an MCS, andwhether STBC is used or not, for each individual STA) may not beincluded in HE-SIG-A field. Although the individual parameters may beincluded in HE-SIG-B field, information about the number of spatialstreams and information indicating whether STBC is used or not, need tobe transmitted before a HE-LTF field because the number of spatialstreams and the information indicating whether STBC is used or not aresignificant to determination of configuration information about apreamble and a PSDU in a HE PPDU frame format (e.g., the number ofHE-LTF elements is determined according to a combination of the numberof spatial streams and the information indicating whether STBC is usedor not). For this purpose, a HE PPDU frame format as illustrated in FIG.15 may be used for a UL HE PPDU transmission.

FIG. 15 depicts another exemplary HE PPDU frame format according to thepresent disclosure. The HE PPDU frame format illustrated in FIG. 15 ischaracterized in that a structure of HE-SIG-A, HE-SIG-B, and HE-SIG-Cfields similar to that in FIG. 12 is used for a UL PPDU transmission.

As described before, if a UL MU-MIMO-mode or OFDMA-mode transmission isperformed by triggering of an AP (according to common/individualparameters provided by the AP), an individual STA may not need to reportan individual parameter to the AP. In this case, one or more of aHE-SIG-B field, a HE-SIG-C field, and a first HE-LTF element (i.e., aHE-LTF between a HE-STF field and a HE-SIG-B field) illustrated in FIG.15 may not be present. In this case, a description of each field givenbelow may be applicable only in the presence of the field.

In the example of FIG. 15, a HE-SIG-A field is transmitted per channel(i.e., per 20-MHz channel) and may include transmission parameterscommon to simultaneously transmitted HE PSDUs. Since the sameinformation is transmitted in the fields from the L-STF to HE-SIG-A inUL PPDUs transmitted by HE STAs allocated to subchannels, the AP mayreceive the same signals from the plurality of STAs successfully.

A HE-SIG-B field is transmitted per subchannel in one channel. TheHE-SIG-B field may have an independent parameter value according to thetransmission characteristics of a HE PSDU transmitted on eachsubchannel. The HE-SIG-B field may include spatial stream allocationinformation and information indicating whether STBC is used or not, foreach subchannel. If MU-MIMO is applied to a subchannel (i.e., if aplurality of STAs perform transmission on a subchannel), the HE-SIG-Bfield may include a common parameter for the plurality of STAs paired onthe subchannel.

A HE-SIG-C field is transmitted on the same subchannel as the HE-SIG-Bfield and may include information about an MCS and a packet length. IfMU-MIMO is applied to a subchannel (i.e., if a plurality of STAs performtransmission on a subchannel), the HE-SIG-C field may include respectiveindividual parameters for each of the plurality of STAs paired on thesubchannel.

Similar to DL MU-MIMO-mode or OFDMA-mode HE PPDU transmission, iftransmission of PSDUs start at different time points on subchannels inUL MU-MIMO-mode or OFDMA-mode HE PPDU transmission, and if OFDM symbolsare not aligned accordingly, then the implementation complexity of an APthat receives a plurality of PSDUs is increased. To solve this problem,‘the number of HE-LTFs may be determined for all subchannels accordingto the maximum of the numbers of HE LTFs required according to the totalnumbers of spatial streams transmitted on each subchannel for a set ofHE STAs allocated to each of subchannels’ as described with reference tothe example of FIG. 11.

This feature may mean that the HE-LTF field start at the same time pointand end at the same time point across all users (i.e., HE STAs) in ULMU-MIMO-mode or OFDMA-mode transmission. Or it may be said that theHE-LTF sections of a plurality of subchannels have the same lengthacross all HE STAs in UL MU-MIMO-mode or OFDMA-mode transmission. Or itmay be said that each of the HE-LTF sections of a plurality ofsubchannels includes the same number of HE-LTF elements across all HESTAs in UL MU-MIMO-mode or OFDMA-mode transmission. Therefore, PSDUtransmission timings are synchronized between a plurality of subchannelsacross all HE STAs in UL MU-MIMO-mode or OFDMA-mode transmission.

In the HE PPDU frame format supporting UL MIMO-mode or OFDMA-modetransmission illustrated in FIG. 15, the L-STF, L-LTF, L-SIG, andHE-SIG-A fields may include 4.0-μs OFDM symbols based on 64-FFT. OneOFDM symbol has a GI of 0.8 μs. In the present description, a GI valueapplied to the L-STF, L-LTF, L-SIG, and HE-SIG-A fields is defined asG1. Excluding the GI, the L-STF, L-LTF, L-SIG, and HE-SIG-A fields maybe configured as 3.2-μs OFDM symbols based on 64-FFT.

In the example of FIG. 15, a HE-STF field, a HE-LTF field, a HE-SIG-Bfield, HE-LTF elements(s) in a HE-LTF section, a HE-SIG-C field and aPSDU may include 16-μs OFDM symbols based on 256-FFT. The OFDM symbolduration may be changed according to a GI value. Two types of GI valuesmay be defined for one OFDM symbol for different time periods. A GIvalue applied to the OFDM symbols of the HE-STF field, the HE-LTF field,the HE-SIG-B field, the HE-LTF elements(s) in the HE-LTF section, andthe HE-SIG-C field is defined as G2 and a GI value applied to the OFDMsymbols of the PSDU is defined as G3. Excluding the GIs, the HE-STFfield, the HE-LTF field, the HE-SIG-B field, and the PSDU may include12.8-μs OFDM symbols based on 256-FFT.

The values of G2 and G3 may be equal or different. If G2 and G3 areequal, G2 and G3 may be defined as one parameter without distinguishingG2 from G3. In one embodiment, unlike G1, G2 and G3 may vary accordingto each transmitted PPDU transmission vector, rather than being fixedvalues (i.e. predetermined values known to both a transmitter and areceiver). This is because the lengths of the HE-STF, the HE-LTF, theHE-SIG-B, the HE-LTF element(s) in a HE-LTF section, and the HE-SIG-C towhich G2 is applied may vary according to a PPDU transmission vector andthe length of the PSDU to which G3 is applied may also vary according tothe PPDU transmission vector.

In another example, the G1 applied to the L-STF, L-LTF, L-SIG, andHE-SIG-A fields (to which 64-FFT is applied) may be a fixed value (i.e.,a predefined value known to both a transmitter and a receiver) and oneof G2 and G3 (if G2 and G3 are equal, they may be defined as oneparameter) applied to the following fields (i.e., the HE-STF, HE-LTF,HE-SIG-B, HE-SIG-C, and PSDU to which 256-FFT is applied) may beconfigured or indicated as a variable value (e.g., one of 3.2 μs, 1.6μs, 0.8 μs, and 0.4 μs).

More specifically, G1 may have a fixed value (i.e. a predefined valueknown to both a transmitter and a receiver) of 0.8,μs, G2 may be a valueselected or indicated from among 3.2 μs, 1.6 μs, 0.8 μs, and 0.4 μs, andG3 may be a value selected or indicated from among 3.2 μs , 1.6 μs, 0.8μs, and 0.4 μs. Also, G1 may be a fixed value (i.e. a predefined valueknown to both a transmitter and a receiver) of 0.8 μs, and G2 or G3 maybe a value selected or indicated from among 3.2 μs, 1.6 μs, 0.8 μs, and0.4 μs. G1 does not require signaling because G1 is a fixed value, andsignaling information indicating G2 and G3 may be provided to the AP. Ifa HE STA performs UL transmission according to triggering of the AP (orbased on parameters provided by the AP), the HE-STA does not need toindicate the value of G2 or G3 to the AP.

G2 and G3 are applied commonly across all OFDM symbols transmittedduring a corresponding time period and across all subchannels.Accordingly, PSDU transmission timings may be synchronized, and OFDMsymbol timings may be synchronized. For example, it is not allowed thata 3.2-μs G2 value is applied to a subchannel during a specific timeperiod, while a 1.6-μs or 0.8-μs G2 value is applied to othersubchannels during the same time period. Rather, the same 3.2-μs G2value may be applied to other subchannels during the same time period.In a similar example, it is not allowed that a 1.6-μs G3 value isapplied to a subchannel during a specific time period, while a 3.2-μs or0.8-μs G3 value is applied to other subchannels during the same timeperiod. Rather, the same 1.6-μs G3 value may be applied to othersubchannels during the same time period.

In the case where a HE PPDU frame format having HE-LTF sections ofdifferent lengths for subchannels is used (i.e., in the case where ‘thenumber of HE-LTFs is not determined for each subchannel based on themaximum of the numbers of HE-LTFs required according to the totalnumbers of spatial streams transmitted on subchannels in a set of HESTAs allocated to each of the subchannels’), if the values of G2 and G3are different, a PSDU is transmitted on each subchannel at a differenttime point and OFDM symbol timings are not synchronized. Therefore, thesame values for G2 and G3 may need to be selected or indicated in thiscase.

In the case where a HE PPDU frame format having HE-LTF sections of thesame length for subchannels is used (i.e., in the case where ‘the numberof HE-LTFs is determined for each subchannel based on the maximum of thenumbers of HE-LTFs required according to the total numbers of spatialstreams transmitted on subchannels in a set of HE STAs allocated to eachof the subchannels’), even though the values of G2 and G3 are different,PSDUs are transmitted on the subchannels at the same time point, withoutcausing discrepancy between OFDM symbol timings. Therefore, selection orindication of different values for G2 and G3 does not cause a problem.However, even in this case, selection or indication of the same valuesfor G2 and G3 is not excluded.

In the example of FIG. 15, OFDM symbol durations S1, S2, and S3 may beapplied respectively to time periods to which the GIs G1, G2, and G3 areapplied.

As described before, a plurality of STAs may simultaneously transmitPSDUs in a HE PPDU frame format on their allocated subchannels or ontheir allocated spatial streams to an AP (i.e., referred to as ULMU-MIMO or OFDMA transmission or “UL MU transmission”) and maysimultaneously receive PSDUs in the HE PPDU frame format on theirallocated subchannels on their allocated spatial streams from the AP(i.e., referred to as DL MU-MIMO or OFDMA transmission or “DL MUtransmission”).

FIGS. 16 and 17 depict operating channels in a WLAN system.

Basically, the WLAN system may support a single channel having abandwidth of 20 MHz as a BSS operating channel. The WLAN system may alsosupport a BSS operating channel having a bandwidth of 40 MHz, 80 MHz, or160 MHz by bonding a plurality of contiguous 20-MHz channels (refer toFIG. 16). Further, the WLAN system may support a BSS operating channelhaving a bandwidth of 160 MHz including non-contiguous 80-MHz channels(called a bandwidth of 80+80 MHz) (refer to FIG. 17).

As illustrated in FIG. 16, one 40-MHz channel may include a primary20-MHz channel and a secondary 20-MHz channel which are contiguous. One80-MHz channel may include a primary 40-MHz channel and a secondary40-MHz channel which are contiguous. One 160-MHz channel may include aprimary 80-MHz channel and a secondary 80-MHz channel which arecontiguous. As illustrated in FIG. 17, one 80+80-MHz channel may includea primary 80-MHz channel and a secondary 80-MHz channel which arenon-contiguous.

A primary channel is defined as a common channel for all STAs within aBSS. The primary channel may be used for transmission of a basic signalsuch as a beacon. The primary channel may also be a basic channel usedfor transmission of a data unit (e.g., a PPDU). If a STA uses a channelwidth larger than the channel width of the primary channel, for datatransmission, the STA may use another channel within a correspondingchannel, in addition to the primary channel. This additional channel isreferred to as a secondary channel.

A STA according to an Enhanced Distributed Channel Access (EDCA) schememay determine a transmission bandwidth (or a transmission channel width)as follows.

Upon generation of a transmission frame, a STA (e.g., an AP or a non-APSTA) may perform a back-off procedure on a primary channel in order toacquire a Transmission Opportunity (TXOP). For this purpose, the STA maysense the primary channel during a DIFS or AIFS[i]. If the primarychannel is idle, the STA may attempt to transmit the frame. The STA mayselect a random back-off count, wait for a slot time corresponding tothe selected random back-off count, and then attempt to transmit theframe. The random back-off count may be determined to be a value rangingfrom 0 to CW (CW is a value of a contention window parameter).

When the random back-off procedure starts, the STA may activate aback-off timer according to the determined back-off count and decrementthe back-off count by 1 each time. If the medium of the correspondingchannel is monitored as busy, the STA discontinues the count-down andwaits. If the medium is idle, the STA resumes the count-down. If theback-off timer reaches 0, the STA may determine a transmission bandwidthby checking whether the secondary channel is idle or busy at thecorresponding time point.

For example, the STA may monitor a channel-idle state during apredetermined IFS (e.g., DIFS or AIFS[i]) on the primary channel anddetermine a transmission start timing on the primary channel by therandom back-off procedure. If the secondary channel is idle during aPIFS shortly before the determined transmission start timing of theprimary channel, the STA may transmit a frame on the primary channel andthe secondary channel.

As described above, when the back-off timer reaches 0 for the primarychannel, the STA may transmit an X-MHz mask PPDU (e.g., where X is 20,40, 80, or 160) on channels including an idle secondary channel(s)according to the CCA result of the secondary channel(s).

The X-MHz mask PPDU is a PPDU for which a TXVECTOR parameter, CHBANDWIDTH, is set to CBW X. That is, if the X-MHz mask PPDU can betransmitted, this means that a PPDU satisfying a spectrum mask for X-MHztransmission can be transmitted. The X-MHz mask PPDU may include a PPDUtransmitted in a bandwidth equal to or smaller than X MHz.

For example, if an 80-MHz mask PPDU can be transmitted, this means thata PPDU having a channel width of 80 MHz or a PPDU having a channel widthsmaller than 80 MHz (e.g., 40 MHz, 20 MHz, etc.) can be transmittedwithin a Power Spectral Density (PSD) limit of a spectrum mask for80-MHz transmission.

As described before, if a STA is allowed to start a TXOP and has atleast one MAC Service Data Unit (MSDU) to be transmitted under theAccess Category (AC) of the TXOP allowed for the STA, the STA mayperform one of the following a), b), c), d), or e) (in the followingdescription, FIGS. 16 and 17 may be referred to for a primary channel(i.e., a primary 20-MHz channel) a secondary channel (i.e., a secondary20-MHz channel), a secondary 40-MHz channel, and a secondary 80-MHzchannel):

a) If the secondary channel, the secondary 40-MHz channel, and thesecondary 80-MHz channel are idle during a PIFS shortly before the startof the TXOP, a 160-MHz or 80+80-MHz mask PPDU may be transmitted.

b) If both the secondary channel and the secondary 40-MHz channel areidle during the PIFS shortly before the start of the TXOP, an 80-MHzmask PPDU may be transmitted on a primary 80-MHz channel.

c) If the secondary channel is idle during the PIFS shortly before thestart of the TXOP, a 40-MHz mask PPDU may be transmitted on a primary40-MHz channel.

d) A 20-MHz mask PPDU may be transmitted on the primary 20-MHz channel.

e) A channel access attempt may be resumed by performing a back-offprocedure as in the case where the medium is indicated as busy on theprimary channel by one of physical carrier sensing and virtual carriersensing and a back-off timer has a value of 0.

Now, a description will be given of the features of TXOP limitsapplicable to UL MU transmissions.

A TXOP is an interval of time during which a particularQuality-of-Service (QoS) STA has the right to initiate frame exchangesequences onto the wireless medium. A TXOP holder (or a TXOP owner) is aQoS STA that has either been granted a TXOP by the hybrid coordinator(HC) or successfully contended for a TXOP. A TXOP responder is a STAthat transmits a frame in response to a frame received from a TXOPholder (or a TXOP owner) during a frame exchange sequence, but that doesnot acquire a TXOP in the process.

Under Hybrid Coordination Function (HCF), the basic unit of allocationof the right to transmit onto the wireless medium is the TXOP. Each TXOPis defined by a starting time and a maximum duration (or maximumlength). Here, HCF is a coordination function that combines and enhancesaspects of the contention based and contention free access methods toprovide QoS STAs with prioritized and parameterized QoS access to thewireless medium, while continuing to support non-QoS STAs forbest-effort transfer. The HCF includes the functionality provided byboth Enhanced Distributed Channel Access (EDCA) and HCF ControlledChannel Access (HCCA). EDCA is the prioritized Carrier Sense MultipleAccess with Collision Avoidance (CSMA/CA) access mechanism used by QoSSTAs in a QoS BSS and STAs operating outside the context of a BSS. Thisaccess mechanism is also used by the QoS AP and operates concurrentlywith HCCA.

The duration of a TXOP is the time a STA obtaining a TXOP (i.e., a TXOPholder) maintains uninterrupted control of the medium. The duration of aTXOP includes the time required to transmit frames sent as an immediateresponse to TXOP holder transmissions.

Within a TXOP, a STA may transmit packets separated by SIFS withoutcontending for the wireless medium for transmitting every packet. Toincrease the efficiency for channel access, such as preventing a STAfrom maintaining the TXOP too long, a limitation may be applied to theduration of TXOP. Accordingly, the TXOP holder may ensure that theduration of a TXOP does not exceed the TXOP limit.

The TXOP limits may be provided or configured by an AP. For example, anAP may advertise TXOP Limit field in EDCA Parameter Set element inBeacon and Probe Response frames transmitted by the AP, and the value ofa TXOP limit may be specified as an unsigned integer, in units of 32 μs.

In case of UL MU transmissions, a TXOP holder may be an HE AP and TXOPresponders may be HE STAs. For example, an HE AP may obtain a TXOP totransmit a UL trigger frame, and HE STAs may transmit UL MU PPDU inresponse to the UL trigger frame within the duration of TXOP. Inaddition, the HE AP may transmit acknowledgement (e.g., MU Block Ackframe) to the HE STAs.

The UL trigger frame may be an UL MU-MIMO Poll frame when the follow-upUL MU PPDU includes UL MU-MIMO transmission, or an UL OFDMA Poll framewhen the follow-up UL MU PPDU includes UL OFDMA transmission.

The UL trigger frame may include sufficient information to identify theSTAs transmitting the UL MU PPDUs and information allocating resourcesfor the UL MU PPDUs. For example, the UL trigger frame may include UL MUPPDU Duration information (or a value of the L-SIG Length of the UL MUPPDU) that indicates the duration of the follow-up UL MU PPDUtransmission.

For UL MU transmissions, an HE AP (i.e., the TXOP holder) should ensurethat the duration of a TXOP does not exceed the TXOP limit. For example,the HE AP may or may not transmit an UL trigger frame based on whetherthe time required for a frame exchange sequence exceeds the TXOP limitor not. Alternatively or additionally, the HE AP may adjust the UL MUPPDU Duration information to meet the TXOP limit.

According to a first TXOP limitation example, a TXOP holder (e.g., an HEAP) may not transmit an UL trigger frame, when the time required for thetransmission of the UL MU PPDUs plus a SIFS exceeds the TXOP limit. Inother words, the TXOP holder may not initiate a frame exchange sequenceof an UL trigger and an UL MU PPDU (i.e., not including a controlresponse frame) exceeding the TXOP limit. Such constraints may beapplied to setting a value of the UL MU PPDU Duration information of theUL trigger frame. That is, the UL MU PPDU Duration information, whichindicates the time required for the transmission of the UL MU PPDUs, mayhave a value not exceeding the TXOP limit.

According to a second TXOP limitation example, a TXOP holder (e.g., anHE AP) may not transmit an UL trigger frame, when the time required forthe transmission of the UL MU PPDUs and the associated MU Block Ackframe plus two SIFSs exceeds the TXOP limit. In other words, the TXOPholder may not initiate a frame exchange sequence of an UL trigger, anUL MU PPDU and a MU Block Ack frame (i.e., including a control responseframe) exceeding the TXOP limit. Such constraints may be applied tosetting a value of the UL MU PPDU Duration field of the UL triggerframe. That is, the UL MU PPDU Duration field, which indicates the timerequired for the transmission of the UL MU PPDUs and the associated MUBlock Ack frame plus two SIFSs, may have a value not exceeding the TXOPlimit.

A TXOP limit value may be configured for Access Category (AC) and PHYcharacteristics. By way of example and without any limitation, forOFDM/HT/VHT PHYs, a TXOP limit for AC_Video (AC_VI) may be given as4.096 ms which is longer than a TXOP limit 2.528 ms for AC_Best effort(AC_BE), AC_Background (AC_BK), or AC_Voice (AC_VO).

A TXOP limit may have value of zero (0). When a TXOP limit has value of0, a PPDU satisfying a special condition may be transmitted within thecurrent TXOP. An MU PPDU (e.g., DL MU PPDU or UL MU PPDU) carrying asingle data unit or A-MPDU related to multiple users may be transmittedwithin the current TXOP when a TXOP limit has value of 0. For example, aTXOP limit of 0 indicates that the TXOP holder may transmit or cause tobe transmitted (e.g., as responses) one of PPDU(s) indicated asfollowing 1), 2), 3) and 4) at any rate, within the current TXOP.

1) One or more Single-User (SU) PPDUs carrying fragments of a single MACService Data Unit (MSDU) or MAC Management Protocol Data Unit (MMPDU)

2) An SU PPDU or a VHT MU PPDU or an HE MU PPDU carrying a single MSDU,a single MMPDU, a single Aggregate-MSDU (A-MSDU) or a singleAggregate-MPDU (A-MPDU)

3) A VHT MU PPDU carrying A-MPDUs to different users (a single A-MPDU toeach user) or an HE MU PPDU carrying A-MPDUs to/from different users (asingle A-MPDU to/from each user)

4) A QoS Null frame or PS-Poll frame

A TXOP holder may be required to set a duration of a TXOP within a TXOPlimit. However, a TXOP holder may set a duration of a TXOP exceeding aTXOP limit for exceptional cases. For example, a TXOP holder may exceedthe TXOP limit if it does not transmit more than one Data or Managementframe in the TXOP, and for the case indicated as following 5), 6), 7),8), 9), 10), 11), 12) and 13). Otherwise, a TXOP holder may not exceedthe TXOP limit.

5) Retransmission of an MPDU, not in an A-MPDU consisting of more thanone MPDU

6) Initial transmission of an MSDU under a block ack agreement, wherethe MSDU is not in an A-MPDU consisting of more than one MPDU and theMSDU is not in an A-MSDU

7) Transmission of a Control MPDU (including an uplink multi-userControl MPDU) or a QoS Null MPDU, not in an A-MPDU consisting of morethan one MPDU

8) Initial transmission of a fragment of an MSDU or MMPDU, if a previousfragment of that MSDU or MMPDU was retransmitted

9) Transmission of a fragment of an MSDU or MMPDU fragmented into 16fragments

10) Transmission of an A-MPDU consisting of the initial transmission ofa single MPDU not containing an MSDU and that is not an individuallyaddressed Management frame

11) Transmission of a group addressed MPDU, not in an A-MPDU consistingof more than one MPDU

12) Transmission of a Null Data Packet (NDP)

13) Transmission of a VHT NDP Announcement frame and NDP or transmissionof a Beamforming Report Poll frame, where these fit within the TXOPlimit and it is only the response and the immediately preceding SIFScause the TXOP limit to be exceeded

According to the present disclosure, a TXOP for a frame exchangesequence including UL MU data transmission may have a duration exceedinga TXOP limit for exceptional cases. For example, a TXOP holder mayexceed a TXOP limit when the TXOP holder does not transmit more than acontrol response frame after exceeding the TXOP limit. In other words, aTXOP holder may set a duration of a TXOP exceeding a TXOP limit whenonly a control response frame exceeds a TXOP limit.

FIG. 18 depicts an exemplary operation of TXOP limits for UL MUtransmissions according to the present disclosure.

In step S1810, a STA may acquire a TXOP for initiating a frame exchangesequence including UL MU transmission, for example, UL MU datatransmission from a group of one or more TXOP responders.

A STA that has acquired or granted a TXOP becomes a TXOP holder asdepicted in FIG. 18. A TXOP holder may be an HE AP and a group of one ormore TXOP responders may be a group of one or more STAs.

In step S1820, the TXOP holder may determine if a time required for aframe exchange sequence including UL MU transmission exceeds a TXOPlimit. For example, the TXOP holder may determine if a time required fora frame exchange sequence including an UL trigger, an UL MU transmissionand a control response frame exceeds a TXOP limit. In other words, theTXOP holder may determine if the time required for the transmission ofthe UL MU PPDU and the associated MU Block Ack frame plus two SIFSsexceeds the TXOP limit.

If the time required for the frame exchange sequence does not exceed theTXOP limit, the TXOP holder may determine that the frame exchangesequence is valid and may initiate the frame exchange sequence in stepS1840.

If the time required for the frame exchange sequence exceeds the TXOPlimit, the TXOP holder may determine if a time required for a frameexchange sequence not including a control response frame exceeds a TXOPlimit in step S1830.

For example, the TXOP holder may determine if a time required for aframe exchange sequence including an UL trigger and an UL MUtransmission exceeds a TXOP limit. In other words, the TXOP holder maydetermine if the time required for the transmission of the UL MU PPDUplus a SIFS exceeds the TXOP limit.

If the time required for the frame exchange sequence not including acontrol response frame does not exceed the TXOP limit, the TXOP holdermay determine that the frame exchange sequence is valid and may initiatethe frame exchange sequence in step S1840.

If the time required for the frame exchange sequence not including acontrol response frame exceeds the TXOP limit, the TXOP holder maydetermine that the frame exchange sequence is not valid and may adjust aduration of UL MU transmission to meet the TXOP limit in step S1835.

For example, the TXOP holder may adjust a value of UL MU PPDU Durationfield included in the UL trigger frame, to make the time required fortransmission of the UL trigger frame and the UL MU PPDU does not exceedthe TXOP limit.

Alternatively, step S1835 may be omitted and the TXOP holder may notinitiate the frame exchange sequence if it is determined as invalid.

In step S1840, the TXOP holder may initiate the frame exchange sequence.For example, the TXOP holder may transmit UL trigger frame to a group ofone or more TXOP responders in step S1850.

According to the UL trigger frame, the group of one or more TXOPresponders may transmit UL MU PPDU (e.g., UL MU data transmission).

Here, the TXOP limit may indicate a time on or after the UL MU PPDUtransmission (S1860).

In response to the UL MU PPDU, the TXOP holder may transmit a controlresponse frame (e.g., MU Block Ack frame) to the group of one or moreTXOP responders in step S1870.

In the exemplary operation of FIG. 18, step S1820 may be omittedaccording to the first TXOP limitation example, or step S1830 may beomitted according to the second TXOP limitation example as describedabove.

FIG. 19 depicts an exemplary frame exchange sequence with TXOP limitsfor UL MU transmissions according to the present disclosure.

In the example of FIG. 19, the frame exchange sequence of an UL triggerframe (e.g., an UL MU-MIMO Poll frame, or an UL OFDMA Poll frame), an ULMU PPDU (e.g., an UL MU PPDU including UL MU-MIMO transmissions or ULOFDMA transmissions), and a Block ACK frame does not exceed the TXOPlimit.

According to the first TXOP limitation example, the TXOP holder maydetermine if the frame exchange sequence of an UL trigger and an UL MUPPDU (i.e., not including a control response frame) exceeds the TXOPlimit. In other words, the TXOP holder may determine if the timerequired for the transmission of the UL MU PPDU plus a SIFS exceeds theTXOP limit. In the example of FIG. 19, the frame exchange sequence of anUL trigger and an UL MU PPDU does not exceed the TXOP limit, or the timerequired for the transmission of the UL MU PPDU plus a SIFS does notexceed the TXOP limit. Accordingly, the frame exchange sequence of FIG.19 is valid under TXOP limits for UL MU transmissions, and the TXOPholder may transmit the UL trigger frame to start the frame exchangesequence.

According to the second TXOP limitation example, the TXOP holder maydetermine if the frame exchange sequence of an UL trigger, an UL MU PPDUand a MU Block Ack frame (i.e., including a control response frame)exceeds the TXOP limit. In other words, the TXOP holder may determine ifthe time required for the transmission of the UL MU PPDU and theassociated MU Block Ack frame plus two SIFSs exceeds the TXOP limit. Inthe example of FIG. 19, the frame exchange sequence of an UL trigger, anUL MU PPDU and a MU Block Ack frame does not exceed the TXOP limit, orthe time required for the transmission of the UL MU PPDU and theassociated MU Block Ack frame plus two SIFSs does not exceed the TXOPlimit. Accordingly, the frame exchange sequence of FIG. 19 is validunder TXOP limits for UL MU transmissions, and the TXOP holder maytransmit the UL trigger frame to start the frame exchange sequence.

FIG. 20 depicts another exemplary frame exchange sequence with TXOPlimits for UL MU transmissions according to the present disclosure.

In the example of FIG. 20, the frame exchange sequence of an UL triggerframe (e.g., an UL MU-MIMO Poll frame, or an UL OFDMA Poll frame), an ULMU PPDU (e.g., an UL MU PPDU including UL MU-MIMO transmissions, or ULOFDMA transmissions), and a Block ACK frame exceeds the TXOP limit. Morespecifically, the frame exchange sequence of the UL trigger and the ULMU PPDU (i.e., not including a control response frame) does not exceedthe TXOP limit, but the frame exchange sequence of the UL trigger, theUL MU PPDU and the MU Block Ack frame (i.e., including a controlresponse frame) exceeds the TXOP limit.

According to the first TXOP limitation example, the TXOP holder maydetermine if the frame exchange sequence of an UL trigger and an UL MUPPDU (i.e., not including a control response frame) exceeds the TXOPlimit. In other words, the TXOP holder may determine if the timerequired for the transmission of the UL MU PPDU plus a SIFS exceeds theTXOP limit. In the example of FIG. 20, the frame exchange sequence of anUL trigger and an UL MU PPDU does not exceed the TXOP limit, or the timerequired for the transmission of the UL MU PPDU plus a SIFS does notexceed the TXOP limit. Accordingly, the frame exchange sequence of FIG.20 is valid, so long as the TXOP holder transmits only a control frameafter exceeding a TXOP limit. More specifically, even though the frameexchange sequence including a control response frame exceeds the TXOPlimit, the frame exchange sequence is valid when what exceeding the TXOPlimit is only a control response frame.

According to the second TXOP limitation example, the TXOP holder maydetermine if the frame exchange sequence of an UL trigger, an UL MU PPDUand a MU Block Ack frame (i.e., including a control response frame)exceeds the TXOP limit. In other words, the TXOP holder may determine ifthe time required for the transmission of the UL MU PPDU and theassociated MU Block Ack frame plus two SIFSs exceeds the TXOP limit. Inthe example of FIG. 20, the frame exchange sequence of an UL trigger, anUL MU PPDU and a MU Block Ack frame exceeds the TXOP limit, or the timerequired for the transmission of the UL MU PPDU and the associated MUBlock Ack frame plus two SIFSs exceeds the TXOP limit. Accordingly, theframe exchange sequence of FIG. 20 is not valid under TXOP limits for ULMU transmissions, the TXOP holder may not transmit the UL trigger frame,or may adjust a value of UL MU PPDU Duration information (or a value ofthe L-SIG Length of the UL MU PPDU) included in the UL trigger frame tomeet the TXOP limit.

FIG. 21 depicts another exemplary frame exchange sequence with TXOPlimits for UL MU transmissions according to the present disclosure.

In the example of FIG. 21, the frame exchange sequence of an UL triggerframe (e.g., an UL MU-MIMO Poll frame, or an UL OFDMA Poll frame), an ULMU PPDU (e.g., an UL MU PPDU including UL MU-MIMO transmissions, or ULOFDMA transmissions), and a Block ACK frame exceeds the TXOP limit. Morespecifically, the frame exchange sequence of the UL trigger and the ULMU PPDU exceeds the TXOP limit.

According to the first TXOP limitation example, the TXOP holder maydetermine if the frame exchange sequence of an UL trigger and an UL MUPPDU (i.e., not including a control response frame) exceeds the TXOPlimit. In other words, the TXOP holder may determine if the timerequired for the transmission of the UL MU PPDU plus a SIFS exceeds theTXOP limit. In the example of FIG. 21, the frame exchange sequence of anUL trigger and an UL MU PPDU exceeds the TXOP limit, or the timerequired for the transmission of the UL MU PPDU plus a SIFS exceeds theTXOP limit. Accordingly, the frame exchange sequence of FIG. 21 is notvalid under TXOP limits for UL MU transmissions, the TXOP holder may nottransmit the UL trigger frame, or may adjust a value of UL MU PPDUDuration information (or a value of the L-SIG Length of the UL MU PPDU)included in the UL trigger frame to meet the TXOP limit. Morespecifically, the frame exchange sequence is not valid when more than acontrol response frame exceeds the TXOP limit.

According to the second TXOP limitation example, the TXOP holder maydetermine if the frame exchange sequence of an UL trigger, an UL MU PPDUand a MU Block Ack frame (i.e., including a control response frame)exceeds the TXOP limit. In other words, the TXOP holder may determine ifthe time required for the transmission of the UL MU PPDU and theassociated MU Block Ack frame plus two SIFSs exceeds the TXOP limit. Inthe example of FIG. 21, the frame exchange sequence of an UL trigger, anUL MU PPDU and a MU Block Ack frame exceeds the TXOP limit, or the timerequired for the transmission of the UL MU PPDU and the associated MUBlock Ack frame plus two SIFSs exceeds the TXOP limit. Accordingly, theframe exchange sequence of FIG. 21 is not valid under TXOP limits for ULMU transmissions, the TXOP holder may not transmit the UL trigger frame,or may adjust a value of UL MU PPDU Duration information (or a value ofthe L-SIG Length of the UL MU PPDU) included in the UL trigger frame tomeet the TXOP limit.

FIG. 22 depicts another exemplary frame exchange sequence with TXOPlimits for UL MU transmissions according to the present disclosure.

In the example of FIG. 22, the frame exchange sequence of a DL MU PPDU(e.g., an HE PPDU including DL OFDMA Data frames), and an UL MU PPDU(e.g., an HE PPDU including UL OFDMA ACK frame) exceeds the TXOP limit.More specifically, the DL MU PPDU does not exceed the TXOP limit, butthe frame exchange sequence of the DL MU PPDU and the UL MU PPDU whichis a control response frame exceeds the TXOP limit. Here, the DL MU Dataframe may correspond to or include an UL trigger frame in that itelicits immediate UL control response frame transmission.

For a frame exchange sequence including UL MU ACK transmission, the TXOPholder may determine if a DL MU PPDU (i.e., not including a controlresponse frame) exceeds the TXOP limit. In the example of FIG. 22, a DLMU PPDU does not exceed the TXOP limit. Accordingly, the frame exchangesequence of FIG. 22 is valid. More specifically, even though the frameexchange sequence including a control response frame exceeds the TXOPlimit, the frame exchange sequence is valid when what exceeding the TXOPlimit is only a control response frame.

Now, a description will be given of the features of back-off operationsapplicable to UL MU transmissions.

FIG. 23 depicts an exemplary operation of backoff procedure for UL MUtransmissions according to the present disclosure.

For UL MU transmissions, an AP may transmit a UL trigger frame (e.g., anUL MU-MIMO Poll frame, or an UL OFDMA Poll frame) to STAs. In responseto the UL trigger frame, the STAs may transmit an UL MU PPDU asindicated by the trigger frame. The AP may transmit a control responseframe to STAs that transmitted the UL MU PPDU. Such frame exchangesequence (i.e., UL trigger, UL MU transmission and a control responseframe) may be performed within a duration of a TXOP.

In step S2310, an AP may transmit Target Poll Transmission Time (TPTT)information to a group of one or more STAs.

Specifically, an AP may configure or determine a transmission time of aUL trigger frame (or an UL MU-MIMO/OFDMA Poll frame), and an expectedtransmission time of a UL trigger frame (or an UL MU-MIMO/OFDMA Pollframe) may be referred to as a TPTT.

An AP may configure or determine one or more TPTTs. At a TPTT, the APmay schedule an UL trigger frame (or an UL MU-MIMO/OFDMA Poll frame)transmission. A TPTT information element specifying informationindicating one or more TPTTs may be included in a Beacon frame.

A TPTT information element may specify a Target Beacon Transmission Time(TBTT). For example, a TPTT indicated by the TPTT information elementmay be specified by a number of TBTTs, or may be specified by an offsetto a certain TBTT (e.g., a next TBTT)

A STA receiving a Beacon frame including a TPTT information element maylisten to an UL trigger frame (or an UL MU-MIMO/OFDMA Poll frame)transmitted at each of one or more TPTTs as indicated by the TPTTinformation element.

A TPTT may be configured within a TXOP. However, a TXOP holder may notextend TXOP to include a TPTT in order to improve a throughput andenergy efficiency of a STA. Specifically, a TXOP holder may not change aduration of TXOP that has been already obtained by or granted to theTXOP holder, if the changed duration of the TXOP overlaps a TPTT. Forexample, if a STA receiving a Beacon frame including the TPTTinformation element already owns a TXOP before the TPTT, the STA may notallowed to extend the corresponding TXOP by crossing the TPTT.

Here, a STA may consider TPTT information provided by a BSS with whichthe STA is associated, but the STA may disregard or discard TPTTinformation provided by a different BSS with which the STA is notassociated.

In step S2320, the AP may transmit an UL trigger frame at a TPTT.

The UL trigger frame may include user identification information thatspecify one or more STAs being elicited to transmit an UL MU PPDU.

In addition, an UL trigger frame (or an UL MU-MIMO/OFDMA Poll frame) maybe used for invoke an UL MU transmission from anonynous users. Forexmaple, an UL trigger frame may include an empty list of the grantedSTAs. That is, an UL trigger frame may be used for allowing randomaccess of unspecified STAs to participate in an UL MU transmission onresources allocated by the UL trigger frame. A Beacon frame may indicateone or more TPTTs of one or more UL trigger frames that allocateresources for random access.

An UL trigger frame without any condition for participating in an UL MUtransmission may invoke an UL MU tranmission of anonymous users.However, an UL trigger frame may include a certain condition forparticipating in the UL MU transmission. Accordingly, among anonymoususers, STAs being allowed to participate in the UL MU transmission maybe restricted to a group of candidate STAs that satisfy the conditionincluded in the UL trigger frame.

For example, one of conditions to restrict the candidate STAsparticipating in the UL MU transmission may cover or include one or moreaccess categories for the UL MU transmission. When an UL trigger framefor an UL MU transmission from anonymous users (e.g., an UL triggerframe without user identification information) includes informationindicating a certain access category, a STA having a buffered framematching the access category included in the UL trigger frame areeligible to respond to the UL trigger frame and may participate in theUL MU transmission.

In step S2330, a STA may suspend backoff procedure and store backofffunction state at the TPTT or at receiving the UL trigger frame.

Specifically, a STA performing channel access according to EDCA schememay perform a back-off procedure on a channel in order to acquire aTXOP. Multiple STAs may perform channel access according to EDCA schemeat the same time based on their own EDCA parameters (e.g., backoffcounter, Contention Window (CW), QoS Short Retry Counter (QSRC), QoSLong Retry Counter (QLRC), etc.).

While STAs are performing backoff procedures on their own, at TPTT or ata reception time of UL trigger frame, each STA performing channel accessaccording to EDCA scheme may suspend an operation of its EDCA Function(EDCAF), and stores backoff function state of EDCA parameters (e.g.,backoff counter value, CW for an access category (CW[AC]), QSRC for anaccess category (QSRC[AC]), QLRC for an access category (QLRC[AC]),etc.).

In step S2340, STAs may transmit UL MU PPDU to the AP. For example, theSTAs participating in the UL MU transmission may be identified by the ULtrigger frame. Additionally or alternatively, the STAs participating inthe UL MU transmission may be unidentified by the UL trigger frame(i.e., the UL trigger frame elicits UL MU transmission using randomaccess).

Also, resource units for transmitting UL MU PPDU may be indicated by theUL trigger frame. For example, resource unit(s) (or subchannel(s)) maybe explicitly allocated to one or more identified STAs participating inthe UL MU transmission. Additionally or alternatively, resource unit(s)(or subchannel(s)) may be randomly selected, among resource unitsallocated for random access by the UL trigger frame, by anonymous usersthat are eligible to participate in the UL MU transmission. Furtherexamples of resource unit selection for UL random access will bedescribed with referring to FIGS. 24 and 25.

In step S2350, the AP may transmit an ACK frame to STAs. Here, the APmay transmit an ACK frame in response to successfully received UL MUtransmission. For example, if a collision occurs among UL transmissionsof multiple STAs, the AP may not receive the UL transmission and no ACKframe is transmitted to those STAs.

In step S2360, each STA that has transmitted the UL MU PPDU determinesif ACK frame is received. If a STA has failed to receive ACK frame, theSTA may resume backoff procedure that has been suspended in step S2370.If a STA has received ACK frame, the STA may invoke a new backoffprocedure to acquire TXOP in step S2380.

Alternatively or additionally, without checking the successful receptionof ACK frame as in step S2360, at the end of the TXOP controlled orinitiated by UL trigger frame, a STA may restore the previously storedbackoff function state and may resume an operation of EDCAF as in stepS2370. If the previously stored backoff function state is empty for aSTA resuming a backoff procedure at the end of the TXOP, the EDCAF ofthe STA may invoke a backoff procedure, even if no additionaltransmissions are currently queued as in step S2380.

Alternatively or additionally, backoff function state may be changed atthe end of a TXOP. For example, backoff function state may be changedbased on the traffic load or congestion state. An UL MU transmissionfrom anonymous users may be successful when the traffic load orcongestion is not heavy (i.e., when the traffic load is not greater thana reference). An UL MU transmission from anonymous users may not besuccessful when the traffic load or congestion is heavy (i.e., when thetraffic load is greater than the reference). Specifically, if thetraffic load or congestion is not heavy, or after the successfultransmission of an UL MU PPDU, each STA performing EDCA access may resetbackoff function state (e.g., backoff counter, CW[AC], QSRC[AC],QLRC[AC], etc.) instead of unchanging (or restoring) its previouslystored backoff function state. If the traffic load or congestion isheavy, or after the transmission failure of an UL MU PPDU, each STAperforming EDCA access may increase backoff function state (e.g.,backoff counter, CW[AC], QSRC[AC], QLRC [AC], etc.) instead ofunchanging (or restoring) its previously stored backoff function state.

Alternatively or additionally, for UL random access mechanism, if a STAhas failed to receive ACK frame, the STA may invoke a backoff procedurewith new backoff counter value. An exemplary operation of this examplewill be given with referring to FIG. 24.

FIG. 24 depicts an exemplary operation of backoff procedure for ULrandom access according to the present disclosure.

When an UL trigger frame indicates that anonymous users are eligible toparticipate in an UL MU transmission, the UL trigger frame may includeinformation indicating resource unit(s) (or subchannel(s)) for randomaccess. STAs that are eligible to participate in an UL MU transmissionin random access manner may randomly select one or more resource units(or one or more subchannels) among the resource unit(s) (orsubchannel(s)) indicated by the UL trigger frame. After random selectionof resource units, the STAs may start UL MU transmission a SIFS afterthe UL trigger frame.

Random selection of a resource unit may be based on a backoff counter.Specifically, a backoff counter of a STA has a purely random property,so the backoff counter of the STA may be utilized for random selectionof a resource unit. That is, a STA may select a resource unit using afunction of backoff counter.

In the example of FIG. 24, STA1, STA2, STA3 and STA4 performs UL randomaccess based on OFDMA.

An AP may transmit an UL trigger frame eliciting UL random access fromanonymous users. The trigger frame for random access may be referred toas TF-R.

Before receiving the TF-R, STA1, STA2, STA3 and STA4 may be performingbackoff procedures. That is, each STA randomly select a backoff counterand count-down a value of the backoff counter when the medium is idleduring a backoff slot. In the example of FIG. 24, STA1 selects a backoffcounter value 4, STA2 selects a backoff counter value 9, STA3 selects abackoff counter value 7, STA4 selects a backoff counter value 9, andeach STA counts down its own backoff counter.

At TPTT or at receiving a TF-R, STAs may suspend their backoffprocedures and store backoff function state at the TPTT or at receivingthe UL trigger frame. Before transmitting UL MU PPDU in response to theTF-R, a STA may select a resource unit (or a subchannel) used fortransmitting an UL MU frame in OFDMA manner.

In the example of FIG. 24, STA1 stores a backoff counter value of 2 atreceiving the TF-R, it may choose a resource unit 2 (subchannel 2) whichcorresponds to the backoff counter value 2. STA2 stores a backoffcounter value of 7 at receiving the TF-R, it may choose a resource unit7 (subchannel 7) which corresponds to the backoff counter value 7. STA3stores a backoff counter value of 5 at receiving the TF-R, it may choosea resource unit 5 (subchannel 5) which corresponds to the backoffcounter value 5. STA2 stores a backoff counter value of 7 at receivingthe TF-R, it may choose a resource unit 7 (subchannel 7) whichcorresponds to the backoff counter value 7. The mapping relationshipbetween the resource units and backoff counter values is exemplary,without limiting the present disclosure.

STA1 may transmit UL MU frame on resource unit 2, and STA 3 may transmitUL MU frame on resource unit 3. STA1 and STA3 may receive ACK framesuccessfully. However, STA2 and STA4 may transmit UL MU frame on thesame resource unit 7. In other words, a collision occurs when STA2 andSTA4 perform UL MU transmission. In that case, an AP may notsuccessfully receive UL MU frame from STA2 and STA4, and no ACK framemay be provided to STA2 and STA4.

STA2 and STA may determine that a collision have been occurred in theirUL random access based on missing ACK frame. Since STA2 and STA4 usedthe same backoff counter value for choosing resource units for randomaccess and stored the backoff counter value at receiving TF-R, acollision may occur again when STA2 and STA4 reuse the stored backoffcounter.

To avoid such collision, a STA that has failed in receiving ACK frame inresponse to UL random access transmission may randomly select itsbackoff counter (i.e., use new backoff counter) when it resumes backoffprocedure. In the example of FIG. 24, STA2 uses a new backoff counter 4when resuming a backoff procedure instead of using the stored backoffcounter value 7. STA4 uses a new backoff counter 8 when resuming abackoff procedure instead of using the stored backoff counter value 7.

According to the present disclosure, a STA may perform CCA on theresource units allocated for UL random access before selecting aresource unit. Specifically, after receiving a TF-R including resourceunit allocation information for UL random access, a STA may check CCA onresource units (or subchannels) allowed for UL random access.

For example, an operation indicated as following a), b) and c) may beapplied for a STA selecting resource unit (or subchannel) for UL randomaccess.

a) A STA may check CCA on the subchannels allocated by the UL triggerframe, resulting in at least one idle subchannel is present.

b) The STA may select a subchannel from the at least one idlesubchannel.

c) The STA may transmit a UL MU frame on the selected subchannel.

Above operation of a), b) and c) is a subchannel selection based on anon-uniform random property. To improve fairness in subchannelselection, an alternative operation indicated as following d), e) and 0may be applied for a STA selecting resource unit (or subchannel) for ULrandom access.

d) A STA may check CCA on the subchannels allocated by the UL triggerframe, resulting in at least one idle subchannel is present.

e) If all of the at least one subchannel is idle, the STA may select asubchannel from the at least one idle subchannel; Otherwise, the STA maynot perform anything or may not be allowed to begin any transmission.

f) The STA may transmit a UL MU frame on the selected subchannel.

Above operation of d), e) and f) allows a subchannel selection only whenall subchannels are idle, and has a low random channel accessprobability. To improve a random access probability, another alternativeoperation indicated as following g), h) and i) may be applied for a STAselecting resource unit (or subchannel) for UL random access.

g) A STA may check CCA on the subchannels allocated by the UL triggerframe, resulting in at least one idle subchannel is present.

h) The STA may select a subchannel from all subchannels (including bothidle subchannel(s) and busy subchannel(s)).

i) If the selected subchannel is idle, the STA may transmit a UL MUframe on the selected subchannel; Otherwise, the STA may not performanything or may not be allowed to begin any transmission.

Additionally or alternatively, a STA may not perform CCA on the resourceunits allocated for UL random access before selecting a resource unit.Specifically, after receiving a TF-R including resource unit allocationinformation for UL random access, a STA may not check any CCA.

For example, an operation indicated as following j) and k) may beapplied for a STA selecting resource unit (or subchannel) for UL randomaccess.

j) A STA may not check any CCA on the subchannels allocated by the ULtrigger frame, and the STA may select a subchannel from all subchannels(including both idle subchannel(s) and busy subchannel(s)) among thesubchannels allocated by the UL trigger frame, regardless of CCA.

k) The STA may transmit a UL MU frame on the selected subchannel.

For the UL random access, if a STA decides to transmit an UL MU frame onthe selected sub-channel, the STA may transmit the UL MU frame to APfrom which it receives a TF-R frame.

Now, a description will be given of the features of UL random access indynamic frequency selection (DFS) channel.

A DFS are features mandated to satisfy requirements in some regulatorydomains for radar detection and uniform channel spreading in the 5 GHzband. DFS may also be used for other purposes, such as automaticfrequency planning. DFS service provides association of STAs with an APbased on the STAs' supported channels, quieting the current channel soit can be tested for the presence of radar with less interference fromother STAs, testing channels for radar before using a channel and whileoperating in a channel, discontinuing operations after detecting radarin the current channel to avoid interference with radar, detecting radarin the current and other channels based on regulatory requirements,requesting and reporting of measurements in the current and otherchannels, selecting and advertising a new channel to assist themigration of a BSS after radar is detected.

An UL OFDMA-based random access may be used in a DFS channel, whensatisfying additional requirements for DFS. DFS requires that a STA haveto listen to a Beacon frame before accessing a wireless medium. Based onthe above, exemplary operation of STA performing UL OFDMA-based randomaccess will be described below, assuming that at least one subchannelamong the subchannels allocated by a TF-R (or granted by an AP) occupiesa DFS channel.

For an UL random access in channels including at least one DFS channeland zero or more non-DFS channels, an unassociated STA receiving a TF-Rmay randomly select a subchannel from all channels granted by the TF-R,if the STA has received a Beacon frame. If the STA has not received aBeacon frame, the STA may not perform anything on any channel granted bythe TF-R (e.g., may not select a subchannel from any channel or may notbegin any transmission on any channel).

According to the above example, the operation may be implemented in asimple manner, but the channel utilization efficiency may be degraded.For example, an unassociated STA that has not received a Beacon frameare not allowed to access a wireless medium even on a non-DFS channel.To improve the channel utilization efficiency, the following additionalor alternative examples may be applied.

For an UL random access in channels including at least one DFS channeland zero or more non-DFS channels, an unassociated STA receiving a TF-Rmay randomly select a subchannel from non-DFS channels granted by theTF-R, if the STA has not received a Beacon frame. However, anunassociated STA receiving a TF-R may not perform anything on DFSchannels granted by the TF-R (e.g., may not select a subchannel from DFSchannels or may not begin any transmission on DFS channels), if the STAhas not received a Beacon frame. In addition, an unassociated STAreceiving a TF-R may randomly select a subchannel from all channelsgranted by the TF-R, if the STA has received a Beacon frame.

According to the above example, non-DFS channels may be too muchoverloaded than DFS-channels. The difference of successful channelaccess probability between non-DFS channels and DFS channels may degradethe overall system performance. To improve the channel utilizationfairness, the following additional or alternative examples may beapplied.

For an UL random access in channels including at least one DFS channeland zero or more non-DFS channels, an unassociated STA receiving a TF-Rmay randomly select a subchannel from all channels granted by the TF-R.If the selected subchannel corresponds to DFS channels, a STA havingreceived a Beacon frame is eligible for an UL random access. A STA thathas not received a Beacon frame is not eligible for an UL random access,and the STA may not perform anything on the selected subchannel (e.g.,may not begin any transmission on the selected subchannel). If theselected subchannel corresponds to non-DFS channels, any STA, regardlessof receiving a Beacon frame, is eligible for an UL random access.

FIG. 25 depicts an exemplary operation of UL random access in DFSchannel according to the present disclosure.

In the example of FIG. 25, STA1 to STA7 receives TF-R from an AP, andperform UL MU transmission on the channels granted by the TF-R. Forexample, the channel granted by the TF-R may include a non-DFS channeland a DFS channel.

A STA receiving a TF-R on a non-DFS channel may select a subchannel fromthe non-DFS channel and transmit a UL MU frame on the selected channelin the non-DFS channel. A STA that has received a Beacon frame andreceives a TF-R on a DFS channel may select a subchannel from the DFSchannel and transmit a UL MU frame on the selected channel in the DFSchannel.

In the example of FIG. 25, After receiving TF-R on a non-DFS channel,each of STA1, STA2 and STA3 may select a subchannel from the non-DFSchannel, and may transmit a UL MU frame on the selected subchannel.STA1, STA2 and STA3 may or may not have received a Beacon channel.

After receiving TF-R on a DFS channel, each of STA4, STA5, STA6 and STA7may select a subchannel from the DFS channel, and may transmit a UL MUframe on the selected subchannel. STA4, STA5, STA6 and STA7 may havereceived a Beacon channel.

The AP may transmit ACK frame on the non-DFS channel and the DFSchannel. The ACK frame includes acknowledgement information for STA1,STA2, STA3, STA4 and STA5. The ACK frame may be duplicated on twochannels.

Now, a description will be given of the features of enhanced multicastand broadcast service.

Multicast and broadcast service may have technical problems such asunreliable multicast, no backoff procedure, the lowest PHY data rate.Specifically, the unreliable multicast includes that no ACK mechanismand retransmission mechanism are applicable to multicast and broadcastservice and no mechanisms like RTS/CTS to solve the hidden node problemare applicable to multicast and broadcast service. The no backoffprocedure includes that the multicast and broadcast service always usesfixed contention window size. The lowest PHY data rate includes that themulticast and broadcast service does not provide any PHY rate adaptationmechanism. To solve the above problems regarding the multicast andbroadcast service, RF combining of CTS and ACK frames may be applied.

FIG. 26 depicts an exemplary RF combining mechanism for enhancedmulticast and broadcast service according to the present disclosure,which may be applicable to IEEE 802.11ax (HEW) environment.

After receiving an RTS frame, the multicast and broadcast receivers maysimultaneously transmit CTS frames. In order to use the RF combining, aninitial state of the scrambler may be set to the same value with theinitial state of the scrambler obtained from the previously received RTSframe. In addition, the Power Management (PM) bit and More Data (MD) bitof CTS frame may be set to 0.

After receiving a Multicast DATA frame, the multicast and broadcastreceivers may simultaneously transmit ACK frames. In order to use the RFcombining, an initial state of the scrambler may be set to the samevalue with the initial state of the scrambler obtained from thepreviously received Multicast DATA frame. In addition, the PowerManagement (PM) bit and More Data (MD) bit of ACK frame may be set to 0.

If an AP transmitting a RTS or a Multicast DATA frame does not receivesa CTS or ACK frame in response to the RTS or the Multicast DATA frame,the AP may perform a backoff procedure with a randomly selected newbackoff counter to retransmit the unresponsive RTS or the unresponsiveMulticast DATA frame.

In addition, RTS frame may include signaling information indicatingsimultaneous transmission of CTS frames, such RTS may be referred to asnew Multicast RTS.

Multicast DATA frame may include signaling information indicatingsimultaneous transmission of ACK frames. For example, a Multicast DATAframe may include a Duration field set to ACK transmission time(ACKTxTime). When the Duration field of the Multicast DATA frame is setto non-zero value, the STAs having the multicast address membership maysimultaneously respond with the ACK frame.

While the afore-described exemplary methods of the present disclosurehave been described as a series of operations for simplicity ofdescription, this does not limit the sequence of steps. In someembodiments, steps may be performed at the same time or in a differentsequence. All of the exemplary steps are not always necessary toimplement the method proposed by the present disclosure.

The foregoing embodiments of the present disclosure may be implementedseparately or combinations of two or more of the embodiments may beimplemented simultaneously, for the afore-described exemplary methods ofthe present disclosure.

The present disclosure includes an apparatus for processing orperforming the method of the present disclosure (e.g., the wirelessdevice and its components described with reference to FIGS. 1, 2, and3).

The present disclosure includes software or machine-executableinstructions (e.g., an operating system (OS), an application, firmware,a program, etc.) for executing the method of the present disclosure in adevice or a computer, and a non-transitory computer-readable mediumstoring the software or instructions that can be executed in a device ora computer.

While various embodiments of the present disclosure have been describedin the context of an IEEE 802.11 system, they are applicable to variousmobile communication systems.

What is claimed is:
 1. A method of facilitating a wireless communicationin a wireless local area network, the method comprising: acquiring atransmission opportunity (TXOP) for initiating a frame exchange sequencethat includes a trigger frame, an uplink frame and a control responseframe; determining whether the frame exchange sequence is valid; andtransmitting the trigger frame to one or more stations (STAs) when theframe exchange sequence is determined to be valid, wherein the frameexchange sequence is valid when transmission of the uplink frame and thecontrol response frame do not exceed a TXOP limit, and wherein thetrigger frame includes an adjusted duration value of the transmission ofthe uplink frame to meet the TXOP limit when the transmission of theuplink frame and the control response frame exceed the TXOP limit. 2.The method of claim 1, further comprising: determining that the frameexchange sequence is not valid when the transmission of the uplink frameand the control response frame exceed the TXOP limit, wherein the frameexchange sequence is not initiated when the trigger frame excludes theadjusted duration value of the transmission of the uplink frame.
 3. Themethod of claim 1, wherein determining whether the frame exchangesequence is valid comprises: when the time required for the frameexchange sequence exceeds the TXOP limit: adjusting a duration value ofthe transmission of the uplink frame included in the trigger frame tomeet the TXOP limit.
 4. The method of claim 1, wherein the frameexchange sequence comprises: receiving an UL MU Physical layer ProtocolData Unit (PPDU) in response to the trigger frame, wherein the UL MUPPDU corresponds to the uplink frame; and transmitting a downlink (DL)PPDU including acknowledgement information of the UL MU PPDU, whereinthe DL PPDU including the acknowledgement information corresponds to thecontrol response frame.
 5. The method of claim 4, wherein: the triggerframe includes information to identify the one or more STAs transmittingthe UL MU PPDU and information allocation resources for the UL MU PPDU.6. The method of claim 4, wherein the time required for the frameexchange sequence corresponds to the time required for transmitting thetrigger frame, the UL MU PPDU and the DL PPDU plus a plurality of ShortInterFrame Space (SIFS) intervals.
 7. The method of claim 4, wherein thetrigger frame includes DL MU data transmissions for the one or moreSTAs, and wherein the UL MU PPDU includes acknowledgement information ofthe DL MU data transmissions.
 8. The method of claim 1, furthercomprising: transmitting a beacon frame including information indicatingone or more target transmission times of one or more trigger frames thatallocates resources for the transmission of the uplink frame.
 9. Themethod of claim 1, further comprising: adjusting a duration of the TXOPwithout crossing a target transmission time of the trigger frame.
 10. Astation for facilitating multi-user communication in a wireless network,the station comprising: one or more memories; and one or more processorscoupled to the one or more memories, the one or more processorsconfigured to cause: acquiring a transmission opportunity (TXOP) forinitiating a frame exchange sequence that includes a trigger frame, anuplink frame and a control response frame; determining whether the frameexchange sequence is valid; and transmitting the trigger frame to one ormore stations (STAs) when the frame exchange sequence is determined tobe valid, wherein the frame exchange sequence is valid when transmissionof the uplink frame and the control response frame do not exceed a TXOPlimit, and wherein the trigger frame includes an adjusted duration valueof the transmission of the uplink frame to meet the TXOP limit when thetransmission of the uplink frame and the control response frame exceedthe TXOP limit.
 11. The station of claim 10, wherein the one or moreprocessors are configured to cause: determining that the frame exchangesequence is not valid when the transmission of the uplink frame and thecontrol response frame exceed the TXOP limit, wherein the frame exchangesequence is not initiated when the trigger frame excludes the adjustedduration value of the transmission of the uplink frame.
 12. The stationof claim 10, wherein the one or more processors are configured to cause:when the time required for the frame exchange sequence exceeds the TXOPlimit: adjusting a duration value of the transmission of the uplinkframe included in the trigger frame to meet the TXOP limit.
 13. Thestation of claim 10, wherein the one or more processors are configuredto cause: transmitting a beacon frame including information indicatingone or more target transmission times of one or more trigger frames thatallocates resources for the transmission of the uplink frame.
 14. Thestation of claim 10, wherein the one or more processors are configuredto cause: adjusting a duration of the TXOP without crossing a targettransmission time of the trigger frame.
 15. A non-transitorycomputer-readable storage medium storing computer-executableinstructions that, when executed by one or more processors, cause one ormore processors to perform operations, the operations comprising:acquiring a transmission opportunity (TXOP) for initiating a frameexchange sequence that includes a trigger frame, an uplink frame and acontrol response frame; determining whether the frame exchange sequenceis valid; and transmitting the trigger frame to one or more stations(STAs) when the frame exchange sequence is determined to be valid,wherein the frame exchange sequence is valid when transmission of theuplink frame and the control response frame do not exceed a TXOP limit,and wherein the trigger frame includes an adjusted duration value of thetransmission of the uplink frame to meet the TXOP limit when thetransmission of the uplink frame and the control response frame exceedthe TXOP limit.
 16. The non-transitory computer-readable storage mediumof claim 15, wherein the operations comprise: determining that the frameexchange sequence is not valid when the transmission of the uplink frameand the control response frame exceed the TXOP limit, wherein the frameexchange sequence is not initiated when the trigger frame excludes theadjusted duration value of the transmission of the uplink frame.
 17. Thenon-transitory computer-readable storage medium of claim 15, wherein theoperations comprise: when the time required for the frame exchangesequence exceeds the TXOP limit: adjusting a duration value of thetransmission of the uplink frame included in the trigger frame to meetthe TXOP limit.
 18. The non-transitory computer-readable storage mediumof claim 15, wherein the operations comprise: transmitting a beaconframe including information indicating one or more target transmissiontimes of one or more trigger frames that allocates resources for thetransmission of the uplink frame.
 19. The non-transitorycomputer-readable storage medium of claim 15, wherein the operationscomprise: adjusting a duration of the TXOP without crossing a targettransmission time of the trigger frame.
 20. The non-transitorycomputer-readable storage medium of claim 15, wherein the operationscomprise: receiving an UL MU Physical layer Protocol Data Unit (PPDU) inresponse to the trigger frame, wherein the UL MU PPDU corresponds to theuplink frame; and transmitting a downlink (DL) PPDU includingacknowledgement information of the UL MU PPDU, wherein the DL PPDUincluding the acknowledgement information corresponds to the controlresponse frame, wherein the time required for the frame exchangesequence corresponds to the time required for transmitting the triggerframe, the UL MU PPDU and the DL PPDU plus a plurality of ShortInterFrame Space (SIFS) intervals.